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  • stability
  • Springer  (134)
  • Nature Publishing Group
  • 2000-2004  (58)
  • 1985-1989  (76)
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  • 1
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    Springer
    Circuits, systems and signal processing 19 (2000), S. 423-435 
    ISSN: 1531-5878
    Keywords: Time-varying autoregressive models ; stability ; smoothness priors ; Tihkonov regularization ; constrained optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The stability of time-varying autoregressive (AR) models is an important issue in such applications as time-varying spectrum estimation and electroencephalography simulation and estimation. In some cases, such as time-varying spectrum estimation, the models that exhibit roots near unit moduli are difficult to use. Thus a tighter stability condition such as stability with a positive margin is needed. A time-varying AR model is stable with a positive margin if the moduli of the roots of the time-varying characteristic polynomial are somewhat less than unity for every time instant. Recently, a new method for the estimation of the time-varying AR models was introduced. This method is based on the interpretation of the underdetermined time-varying prediction equations as an ill-posed inverse problem that is solved by Tikhonov regularization. The method is referred to as the deterministic regression smoothness priors (DRSP) scheme. In this paper, a stabilization method in which the DRSP scheme is augmented with nonlinear stability constrainst is proposed. The problem is formulated so that stability with a positive margin can also be achieved. The problem is solved iteratively with an exterior point algorithm. The performance of the algorithm is studied with a simulation. It is shown that the proposed approach is well suited to stable modeling of signals containing narrowband transitions.
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  • 2
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    Circuits, systems and signal processing 19 (2000), S. 13-25 
    ISSN: 1531-5878
    Keywords: Singular systems ; delay ; consistency condition ; stability ; instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, the general class of singular systems with delay and linear constant coefficient singular systems with delay are discussed. First, several definitions of stability are presented for singular systems with delay, and general sufficient stability conditions and instability conditions are obtained. Second, stability and instability are analyzed for linear constant coefficient singular systems with delay.
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  • 3
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    Computing 35 (1985), S. 85-91 
    ISSN: 1436-5057
    Keywords: 65M05 ; 65M10 ; 65M25 ; Second order ; characteristic difference schemes ; quasilinear hyperbolic systems ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir stellen ein Charakteristikenverfahren zweiter Ordnung für die numerische Lösung der Anfangswertaufgabe von quasilinearen hyperbolischen Systemen vor und beweisen die Stabilität des Verfahrens für Systeme mit konstanten Koeffizienten.
    Notes: Abstract We present two-step, second-order explicit characteristic difference schemes for the numerical solution of initialvalue problems for quasilinear hyperbolic system and show that the method is stable for systems with constant coefficients.
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  • 4
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    Computing 35 (1985), S. 325-344 
    ISSN: 1436-5057
    Keywords: 65L05 ; Numerical analysis ; Nyström methods ; stiff problems ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Abstract The stability of adaptive Nyström-Runge-Kutta procedures is studied for a wide class of nonlinear stiff systems of second order differential equations. We show that for a large class of semi-discrete hyperbolic and parabolic problems the restriction of the stepsize is not due to the stiffness of the differential equation. Furthermore we use the scalar test equation $$y'' = - \omega ^2 y + q \cdot e^{iv(t - t_0 )} $$ to derive conditions which ensure that the numerical forced oscillation is in phase with the analytical forced oscillation. The order of adaptive Nyström-Runge-Kutta methods (with a stability-matrix based on a diagonal Padéapproximation) for which the forced oscillation is in phase with its analytical counterpart cannot be greater than two. This barrier of order is not true forr-stage implicit Nyström methods of orderp=2r.
    Notes: Zusammenfassung Für eine umfangreiche Klasse nichtlinearer steifer Differentialgleichungssysteme zweiter Ordnung wird die Stabilität adaptiver Nyström-Runge-Kutta-Verfahren untersucht. Wir zeigen, daß für eine große Klasse semidiskretisierter hyperbolischer und parabolischer Probleme die Restriktion der Schrittweite unabhängig von der Steifheit des Differentialgleichungssystems ist. Weiterhin verwenden wir die skalare Testgleichung $$y'' = - \omega ^2 y + q \cdot e^{iv(t - t_0 )} $$ und geben Bedingungen dafür an, daß die numerische erzwungene Schwingung mit der analytischen erzwungenen Schwingung in Phase ist. Die Konsistenzordnung adaptiver Nyström-Runge-Kutta-Verfahren (mit einer Stabilitätsmatrix, die auf einer diagnolen Padé-Approximation beruht), für die die erzwungene Schwingung mit ihrem analytischen Gegenstück in Phase ist, kann nicht größer als zwei sein. Diese Ordnungsbarriere gilt nicht fürr-stufige implizite Nyström-Methoden der Ordnungp=2r.
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  • 5
    ISSN: 1435-1536
    Keywords: Emulsions ; stability ; interfacial properties of emulsions ; soybean protein ; glycerides ; stabilised O/W emulsions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of chemically modified 7S fraction of soybean protein (7MSPF), and its partial replacement by mono- and di-glycerides in various ratios, on the rate of drop coalescence in concentrated corn oil-in-water emulsions has been investigated. A total emulsifier concentration of 2.0 % (wt/wt) was used. The minimum drop coalescence rate was achieved when using 1.0% (wt/wt) 7MSPF in conjunction with 0.5% (wt/wt) monoglyceride and 0.5 % (wt/wt) di-glyceride at pH 5.5. At other mono-/di-glycerides and protein/glycerides ratios, and at other pHs, the rate of drop coalescence was higher than when 2.0% (wt/wt) 7MSPF was used. The reduction in drop coalescence rate under these conditions is attributed to association of 7MSPF with the glycerides at the oil-water interface. The influence of protein/glycerides ratio on the viscoelastic properties of mixed interfacial films supports this view.
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  • 6
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    Rheologica acta 26 (1987), S. 119-126 
    ISSN: 1435-1528
    Keywords: Maxwell fluid ; planeCouette flow ; stability ; criticalWeissenberg number
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Abstract The stability behaviour of a Maxwell fluid in a simple plane shear flow for a class of special perturbations is investigated. Necessary and sufficient stability criteria, especially a critical Weissenberg number for the stability (We k ≈ 4) are given. The results of the analysis are in qualitative agreement with experimental observations.
    Notes: Zusammenfassung Es wird das Stabilitätsverhalten eines Maxwell-Fluids in einer einfachen ebenen Scherströmung für eine spezielle Störungsklasse untersucht. Notwendige und hinreichende Stabilitätskriterien sowie eine kritische Weissenbergzahl (We k ≈ 4) werden angegeben. Die Ergebnisse der Analyse stehen mit experimentellen Befunden in qualitativer Übereinstimmung.
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  • 7
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    Fire technology 23 (1987), S. 175-185 
    ISSN: 1572-8099
    Keywords: Fire evaluation ; expert ; consensus ; stability ; reliability ; validity ; scaling measurement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract In this article some of the methodological problems associated with using the Delphi technique for the development of a Firesafety Evaluation (Points) Scheme are examined. These problems relate to: questionnaire design, the merits and demerits of Delphi groups versus panel groups, the definition of key terms (such as expert, consensus and stability), the reliability, validity and level of measurement achieved by Likert-type scaling techniques, and the differences in the decisionmaking processes of expert and nonexpert groups.
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  • 8
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    Acta biotheoretica 48 (2000), S. 207-218 
    ISSN: 1572-8358
    Keywords: Dynamical population ; fishing efforts ; metapopulation ; time scales ; aggregation method ; equilibrium ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This work presents a specific stock-effort dynamical model. The stocks correspond to two populations of fish moving and growing between two fishery zones. They are harvested by two different fleets. The effort represents the number of fishing boats of the two fleets that operate in the two fishing zones. The bioeconomical model is a set of four ODE's governing the fishing efforts and the stocks in the two fishing areas. Furthermore, the migration of the fish between the two patches is assumed to be faster than the growth of the harvested stock. The displacement of the fleets is also faster than the variation in the number of fishing boats resulting from the investment of the fishing income. So, there are two time scales: a fast one corresponding to the migration between the two patches, and a slow time scale corresponding to growth. We use aggregation methods that allow us to reduce the dimension of the model and to obtain an aggregated model for the total fishing effort and fish stock of the two fishing zones. The mathematical analysis of the model is shown. Under some conditions, we obtain a stable equilibrium, which is a desired situation, as it leads to a sustainable harvesting equilibrium, keeping the stock at exploitable densities.
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  • 9
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    Journal of dynamics and differential equations 1 (1989), S. 269-298 
    ISSN: 1572-9222
    Keywords: Geometric mechanics ; reduction ; stability ; chaos ; rigid body dynamics ; periodic orbits ; 58F
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We give a complete bifurcation and stability analysis for the relative equilibria of the dynamics of three coupled planar rigid bodies. We also use the equivariant Weinstein-Moser theorem to show the existence of two periodic orbits distinguished by symmetry type near the stable equilibrium. Finally we prove that the dynamics is chaotic in the sense of Poincaré-Birkhoff-Smale horseshoes using the version of Melnikov's method suitable for systems with symmetry due to Holmes and Marsden.
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  • 10
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    Queueing systems 34 (2000), S. 1-35 
    ISSN: 1572-9443
    Keywords: multiple access ; CDMA ; rates of convergence ; stability ; functional limit theorems ; transient analysis ; Markov-modulated capture channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We consider the slotted ALOHA protocol on a channel with a capture effect. There are M 〈 ∞ users each with an infinite buffer. If in a slot, i packets are transmitted, then the probability of a successful reception of a packet is q i. This model contains the CDMA protocols as special cases. We obtain sufficient rate conditions, which are close to necessary for stability of the system, when the arrival streams are stationary ergodic. Under the same rate conditions, for general regenerative arrival streams, we obtain the rates of convergence to stationarity, finiteness of stationary moments and various functional limit theorems. Our arrival streams contain all the traffic models suggested in the recent literature, including the ones which display long range dependence. We also obtain bounds on the stationary moments of waiting times which can be tight under realistic conditions. Finally, we obtain several results on the transient performance of the system, e.g., first time to overflow and the limits of the overflow process. We also extend the above results to the case of a capture channel exhibiting Markov modulated fading. Most of our results and proofs will be shown to hold also for the slotted ALOHA protocol without capture.
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  • 11
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    Celestial mechanics and dynamical astronomy 78 (2000), S. 227-241 
    ISSN: 1572-9478
    Keywords: stability ; normal form ; spin-orbit resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider a model of spin-orbit interaction, describing the motion of an oblate satellite rotating about an internal spin-axis and orbiting about a central planet. The resulting second order differential equation depends upon the parameters provided by the equatorial oblateness of the satellite and its orbital eccentricity. Normal form transformations around the main spin-orbit resonances are carried out explicitly. As an outcome, one can compute some invariants; the fact that these quantities are not identically zero is a necessary condition to prove the existence of nearby periodic orbits (Birkhoff fixed point theorem). Moreover, the nonvanishing of the invariants provides also the stability of the spin-orbit resonances, since it guarantees the existence of invariant curves surrounding the periodic orbit.
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  • 12
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    Journal of computational analysis and applications 2 (2000), S. 293-308 
    ISSN: 1572-9206
    Keywords: parabolic equations ; ADI scheme ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An ADI scheme for solving three-dimensional parabolic equations withfirst-order derivatives and variable coefficients has been developed basedon our previous papers and the idea of the modified upwind differencescheme. This ADI scheme is second-order accurate and unconditionallystable. Further, a small parameter can be chosen which makes it suitablefor simulating fast-transient phenomena or for computations on fine spatialmeshes. The method is illustrated with numerical examples.
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  • 13
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    Queueing systems 36 (2000), S. 327-349 
    ISSN: 1572-9443
    Keywords: multiclass networks ; networks with feedback ; Skorokhod Problem ; Skorokhod Mapping ; Lipschitz continuity ; stability ; load conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We consider a four-class two-station network with feedback, with fluid inputs and a head-of-the-line generalized processor sharing discipline at each station. We derive the Skorokhod Problem associated with the network and obtain algebraic sufficient conditions for Lipschitz continuity of the associated Skorokhod Map. This provides the first example of a multiclass network with feedback for which the associated Skorokhod Problem has been proved to be regular. As an elementary application, we show that under the conditions which guarantee Lipschitz continuity the network is stable if and only if the usual load conditions apply.
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  • 14
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    Journal of dynamics and differential equations 12 (2000), S. 117-167 
    ISSN: 1572-9222
    Keywords: singular perturbation ; standing pulses ; stability ; Hopf bifurcation ; reaction-diffusion system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Bifurcation phenomena from standing pulse solutions of the problem $$\varepsilon \tau u_t = \varepsilon ^2 u_{xx} + f(u,v),{\text{ }}v_t = v_{xx} + g(u,v)$$ is considered. ε(〉0) is a sufficiently small parameter and τ is a positive one. It is shown that there exist two types of destabilization of standing pulse solutions when τ decreases. One is the appearance of travelling pulse solutions via the static bifurcation and the other is that of in-phase breathers via the Hopf bifurcation. Furthermore which type of destabilization occurs first with decreasing τ is discussed for the piecewise linear nonlinearities f and g.
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  • 15
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    Catalysis letters 68 (2000), S. 55-58 
    ISSN: 1572-879X
    Keywords: promoting effect ; B2O3 ; Cu/ZnO/Al2O3 catalyst ; methanol synthesis ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The addition of B2O3 to a Cu/ZnO/Al2O3 catalyst increased the activity of the catalyst for methanol synthesis after an induction period during the reaction. The stability of the B2O3-containing Cu/ZnO/Al2O3 catalyst was greatly improved by the addition of a small amount of colloidal silica to the catalyst.
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  • 16
    ISSN: 1572-879X
    Keywords: potassium desorption ; stability ; excitation ; iron catalyst ; Rydberg atoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Well‐characterized catalyst model compounds of KAlO2 and KFeO2 are investigated by thermal desorption of potassium from the material. The desorbing fluxes of ions, atoms and highly excited states (field ionizable Rydberg states) were studied with surface and field ionization detectors in a vacuum apparatus. From the Arrhenius plots the activation energies for desorption of K and K+ were determined. The chemical state of potassium at the surfaces is concluded to be: ionic on KAlO2 (with the K desorption barrier of 1.76 eV) and covalent on KFeO2 (barrier of 2.73 eV). These results agree with the data obtained earlier for industrial catalysts for ammonia and styrene production. They are interpreted in terms of the Schottky cycle, which is completed for KAlO2 and fails for KFeO2. This failure indicates a non‐equilibrium desorption process. K Rydberg states are only found to desorb from KFeO2, in agreement with the suggestion that such states in some way are responsible for the catalytic activity.
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  • 17
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    Journal of dynamics and differential equations 1 (1989), S. 299-325 
    ISSN: 1572-9222
    Keywords: Commodity markets ; time delays ; stability ; Hopf bifurcation ; 34K15 ; 45J05 ; 90A16
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A model for the dynamics of price adjustment in a single commodity market is developed. Nonlinearities in both supply and demand functions are considered explicitly, as are delays due to production lags and storage policies, to yield a nonlinear integrodifferential equation. Conditions for the local stability of the equilibrium price are derived in terms of the elasticities of supply and demand, the supply and demand relaxation times, and the equilibrium production-storage delay. The destabilizing effect of consumer memory on the equilibrium price is analyzed, and the ensuing Hopf bifurcations are described.
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  • 18
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    Set-valued analysis 8 (2000), S. 253-266 
    ISSN: 1572-932X
    Keywords: Hausdorff metric ; linear inequality systems ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we propose a Hausdorff metric to measure the “distance” between two linear inequality systems on a real normed space X. For this topology, which comes through a pseudo-metric in the set Σ of linear inequality systems, the closedness of the feasible set mapping is studied, and at the same time a characterization of the stability of the subset Σ c of consistent sytems is given.
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  • 19
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    Annals of operations research 99 (2000), S. 251-265 
    ISSN: 1572-9338
    Keywords: stochastic programming ; bond portfolio management ; interest ratescenarios ; stability ; sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The bond portfolio management problem is formulated as a multiperiod two-stage or multistage stochastic program based on interest rate scenarios. These scenarios depend on the available market data, on the applied estimation and sampling techniques, etc., and are used to evaluate coefficients of the resulting large scale mathematical program. The aim of the contribution is to analyze stability and sensitivity of this program on small changes of the coefficients – the (scenario dependent) values of future interest rates and prices. We shall prove that under sensible assumptions, the scenario subproblems are stable linear programs and that also the optimal first-stage decisions and the optimal value of the considered stochastic program possess acceptable continuity properties.
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  • 20
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    Applications of mathematics 45 (2000), S. 161-176 
    ISSN: 1572-9109
    Keywords: reaction-diffusion system ; unilateral conditions ; quasivariational inequality ; Leray-Schauder degree ; eigenvalue ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider a reaction-diffusion system of the activator-inhibitor type with unilateral boundary conditions leading to a quasivariational inequality. We show that there exists a positive eigenvalue of the problem and we obtain an instability of the trivial solution also in some area of parameters where the trivial solution of the same system with Dirichlet and Neumann boundary conditions is stable. Theorems are proved using the method of a jump in the Leray-Schauder degree.
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  • 21
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    Advances in computational mathematics 12 (2000), S. 229-250 
    ISSN: 1572-9044
    Keywords: numerical analysis ; shallow water problems ; DIRK methods ; stability ; 65L06 ; 65L20 ; 65M12 ; 65M20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We construct A‐stable and L‐stable diagonally implicit Runge–Kutta methods of which the diagonal vector in the Butcher matrix has a minimal maximum norm. If the implicit Runge–Kutta relations are iteratively solved by means of the approximately factorized Newton process, then such iterated Runge–Kutta methods are suitable methods for integrating shallow water problems in the sense that the stability boundary is relatively large and that the usually quite fine vertical resolution of the discretized spatial domain is not involved in the stability condition.
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  • 22
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    BIT 26 (1986), S. 93-99 
    ISSN: 1572-9125
    Keywords: Primary 65HO5 ; nonlinear equation ; multiple roots ; multipoint iterative methods ; error constant ; stability ; efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A one-parameter family of derivative free multipoint iterative methods of orders three and four are derived for finding the simple and multiple roots off(x)=0. For simple roots, the third order methods require three function evaluations while the fourth order methods require four function evaluations. For multiple roots, the third order methods require six function evaluations while the fourth order methods require eight function evaluations. Numerical results show the robustness of these methods.
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  • 23
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    BIT 27 (1987), S. 424-437 
    ISSN: 1572-9125
    Keywords: 65 L 05 ; 65 L 20 ; stability ; contractivity ; numerical solution of stiff initial value problems in ordinary differential equations ; Runge-Kutta methods ; Rosenbrock methods ; rational Runge-Kutta methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper concerns the stability analysis of numerical methods for approximating the solutions to (stiff) initial value problems. Our analysis includes the case of (nonlinear) systems of differential equations that are essentially more general than the classical test equationU′=λU, with λ a complex constant. We explore the relation between two stability concepts, viz. the concepts of contractivity and weak contractivity. General Runge-Kutta methods, one-stage Rosenbrock methods and a notable rational Runge-Kutta method are analysed in some detail.
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    BIT 40 (2000), S. 62-73 
    ISSN: 1572-9125
    Keywords: Gaussian elimination ; stability ; pivoting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract It has been recently shown that large growth factors might occur in Gaussian Elimination with Partial Pivoting (GEPP) also when solving some plausibly natural systems. In this note we argue that this potential problem could be easily solved, with much smaller risk of failure, by very small (and low cost) modifications of the basic algorithm, thus confirming its inherent robustness. To this end, we first propose an informal model with the goal of providing further support to the comprehension of the stability properties of GEPP. We then report the results of numerical experiments that confirm the viewpoint embedded in the model. Basing on the previous observations, we finally propose a simple scheme that could be turned into (even more) accurate software for the solution of linear systems.
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  • 25
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    BIT 40 (2000), S. 611-639 
    ISSN: 1572-9125
    Keywords: Runge-Kutta methods ; stability ; convergence ; stiff problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper studies the stability and convergence properties of general Runge-Kutta methods when they are applied to stiff semilinear systems y′(t) = J(t)y(t) + g(t, y(t)) with the stiffness contained in the variable coefficient linear part. We consider two assumptions on the relative variation of the matrix J(t) and show that for each of them there is a family of implicit Runge-Kutta methods that is suitable for the numerical integration of the corresponding stiff semilinear systems, i.e. the methods of the family are stable, convergent and the stage equations possess a unique solution. The conditions on the coefficients of a method to belong to these families turn out to be essentially weaker than the usual algebraic stability condition which appears in connection with the B-stability and convergence for stiff nonlinear systems. Thus there are important RK methods which are not algebraically stable but, according to our theory, they are suitable for the numerical integration of semilinear problems. This paper also extends previous results of Burrage, Hundsdorfer and Verwer on the optimal convergence of implicit Runge-Kutta methods for stiff semilinear systems with a constant coefficients linear part.
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  • 26
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    Acta applicandae mathematicae 9 (1987), S. 219-237 
    ISSN: 1572-9036
    Keywords: 34A34 ; 34D99 ; 90A16 ; Nonlinear differential equations ; stability ; growth ; economic dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper analyses the implications of persistent growth upon the stability properties of dynamic models. Besides the traditional concept of asymptotic stability, new stability criteria-strong/weak absolute, strong/weak relative, strong/weak logarithmic stability-are introduced, and global stability conditions for satisfying these criteria are stated for general first-order autonomous differential equations. The conflict between rapidity of growth and the degree of stability is demonstrated. Economic applications of the stability theorems are illustrated within the growth models of Harrod and Solow.
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  • 27
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    Celestial mechanics and dynamical astronomy 47 (1989), S. 333-359 
    ISSN: 1572-9478
    Keywords: symplectic maps ; stability ; normal forms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We prove that non resonant isochronous symplectic maps in a neighborhood of an elliptic fixed point are stable for exponentially long times with the inverse of the distance from the fixed point. In the proof we make use of the majorant series method together with an idea for optimizing remainder estimates first applied to Hamiltonian problems by Nekhoroshev.
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    BIT 40 (2000), S. 226-240 
    ISSN: 1572-9125
    Keywords: Stochastic differential equations ; regularisation ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper is devoted to the numerical analysis of ill-posed problems of evolution equations in Banach spaces using certain classes of stochastic one-step methods. The linear stability properties of these methods are studied. Regularisation is given by the choice of the regularisation parameter as α = $$\sqrt {\tau _n }$$ , where τ n is the stepsize and provides the convergence on smooth initial data. The case of the approximation of well-posed problems is also considered.
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    Archive of applied mechanics 70 (2000), S. 17-29 
    ISSN: 1432-0681
    Keywords: Key words free-surface flow ; solidification ; strip casting ; steady state ; nonuniqueness ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary The paper is concerned with a one-dimensional analysis of plane open-channel flow with continuous solidification. The process is of relevance for recent developments in the casting of steel and other metals. The bottom of the channel consists of a rotating casting roll and a horizontal cooling table, where the solidified material is withdrawn with given velocity. The study is restricted to the region downstream of the top of the casting roll. Surface tension is neglected. In the main part of the analysis inviscid fluid flow is considered since the Reynolds number is very large in the applications. It is found that the steady-state solutions are nonunique in a certain parameter range. In addition to a continuous solution, there are two solutions including hydraulic jumps, with one hydraulic jump being located on the casting roll, the other one on the cooling table. Regarding the stability of the non unique solutions, the evolution of disturbances is investigated numerically as an initial-value problem. It is concluded that the hydraulic jump on the cooling table is unstable, while the other discontinuous solution as well as the continuous solution are stable for sufficiently small disturbances. Which stable solution is attained in the steady state, depends on the history of the process. Friction at the liquid/solid interface is taken into account in the last part of the analysis. A constant friction coefficient is assumed. It is found that the history of the process determines the steady-state solution if, and only if, the friction coefficient is sufficiently small. For larger values of the friction coefficient, the steady-state solution is unique and independent of the history of the transient process. Furthermore, for sufficiently large friction coefficients, stable hydraulic jumps are found, in contrast to the inviscid case, also on the cooling table.
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    Microchimica acta 92 (1987), S. 121-131 
    ISSN: 1436-5073
    Keywords: stability ; molybdenum(VI) ; chelates ; adsorption polarography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of complexes between Mo(VI) and 8-hydroxy-quinoline (oxine) and four oxine derivatives were investigated by multiwavelength molecular absorption spectrometry, potentiometry, and polarography. The following pKOH- and pKNH- values of the ligands and logK 211-values of the complexes MoO2(OH)2L x− (x=1 or 2) were obtained at 25° C and an ionic strength of 1M(NaClO4): 5,7-dinitro8-hydroxyquinoline 4.59, 〈0, 14.50; 7-nitro-8-hydroxyquinoline-5-sulfonic acid 5.34, 0.41, 15.70; 7-iodo-8-hydroxyquinoline-5-sulfonic acid 6.98, 2.62, 17.65; 8-hydroxyquinoline-5-sulfonic acid 8.33, 4.13, 18.71; and 8-hydroxyquinoline 9.62, 5.28, 19.69. A good linearity was found between logK 211 and the sum of the pK-values of the OH- and NH+-groups. The dependence of the peak current of Mo(VI)-determinations by adsorption polarography of the 7-nitro-8-hydroxyquinoline-5-sulfonate complex of Mo(VI) MoO(OH)3L− can quantitatively be described at pH 0.8–2 using the corresponding pK-values and the log K311 of 18.54±0.03, determined by polarography.
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    Journal of intelligent and robotic systems 27 (2000), S. 195-209 
    ISSN: 1573-0409
    Keywords: wall-climbing robot ; electromagnetic grippers ; stability ; additional support element ; sliding and turning over conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Legged-climbing robot is considered. Each foot of the robot has an electromagnet system for robot"s holding on a metal surface. This surface can be both vertical and inclined, including negative slope. Analytical calculation of robot stability under turn over or sliding conditions has been made. Critical slopes have been determined. One of these slopes corresponds to minimal reserve of robot stability towards sliding and another to minimal reserve of robot stability towards turning-over. As total reserve of stability of a robot is always equal to the minimal one of these reserves. Additional support elements of elastic material with high coefficient of friction, along with electromagnet, allows to increase minimal reserve of robot stability towards sliding. The use of such support elements leads to redistributing force of normal support reaction between electromagnet (which surface has low coefficient of friction) and additional support element (which surface has high coefficient of friction). It is just what leads to increasing the total friction force and as a consequence to increasing of minimal reserve of robot stability towards sliding.
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    K-Theory 1 (1987), S. 185-196 
    ISSN: 1573-0514
    Keywords: Quadratic space ; patching diagram ; projective module ; stability
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    Topics: Mathematics
    Notes: Abstract We prove that every quadratic space of sufficiently large index contains a hyperbolic orthogonal summand.
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    K-Theory 2 (1988), S. 1-355 
    ISSN: 1573-0514
    Keywords: Pseudoisotopy ; stability ; Morse theory
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    Topics: Mathematics
    Notes: Abstract The stability theorem states that the suspension map C(M) → C(M X I) defined on the pseudoisotopy space C(M)=Diff(M X I rel M X O U ∂M X I) of a compact smooth n-manifold M is ∼ n/3-connected. This implies that C(M) has the R~ n/3-homotopy type of the stable pseudoisotopy space P(M) which is related to Waldhausen's algebraic K-theory of spaces by Waldhausen's formula A(X) Ω∞S∞(X+) X B2P(X). This paper gives a detailed proof of the smooth stability theorem following ideas by Hatcher for the proof of a PL stability theorem.
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    Letters in mathematical physics 53 (2000), S. 313-320 
    ISSN: 1573-0530
    Keywords: partial differential equations ; nonlinearities ; symmetries ; stability ; minimization
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    Topics: Mathematics , Physics
    Notes: Abstract We suggest a simple but general method of establishing symmetry properties of stable solutions of nonlinear elliptic equations. The method relies on characterization of symmetry breaking with a help of zero modes and on a generalization of the Perron–Frobenius theory.
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    Journal of statistical physics 54 (1989), S. 1427-1427 
    ISSN: 1572-9613
    Keywords: Kink propagation ; kink width ; characteristic functions ; stability ; continuum of modes
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    Topics: Physics
    Notes: Abstract We consider the propagation of kinks in an elastic chain in a bistable or multistable potential under the action of a driving force [M. Büttiker and H. Thomas,Phys. Rev. A 37:235 (1988)]. Each element of the chain is subject to a damping force proportional to its velocity. We show that both the propagation velocity of the kinks as a function of the driving field, and the kink width as a function of propagation velocity, are determined by characteristic functions which depend only on the form of the potential. These functions can be found by considering a single particle moving in the upside-down potential of the chain. The general properties of these functions are studied and illustrated by several examples. The stability of these driven kinks is discussed. Interestingly, we find in addition to the expected discrete localized eigenmodes a two-dimensional continuum of oscillatory modes with a localized envelope.
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    Journal of statistical physics 101 (2000), S. 731-746 
    ISSN: 1572-9613
    Keywords: attractive Bose–Einstein condensates ; nonlinear Schrödinger equation ; stability ; ground state ; variational arguments
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    Topics: Physics
    Notes: Abstract We propose the critical nonlinear Schrödinger equation with a harmonic potential as a model of attractive Bose–Einstein condensates. By an elaborate mathematical analysis we show that a sharp stability threshold exists with respect to the number of condensate particles. The value of the threshold agrees with the existing experimental data. Moreover with this threshold we prove that a ground state of the condensate exists and is orbital stable. We also evaluate the minimum of the condensate energy.
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    Journal of statistical physics 55 (1989), S. 141-156 
    ISSN: 1572-9613
    Keywords: Kosterlitz-Thouless ; Coulomb gas ; hierarchical model ; renormalization group ; screening ; stability ; bifurcation
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    Topics: Physics
    Notes: Abstract A hierarchical version of two-dimensional lattice Coulomb gases is investigated. Forβ〉β c=8π there is a locally stable line of fixed points for the renormalization group (“block charges”) transformations. For $$\beta 〉 \bar \beta _c (\beta _c \leqslant \bar \beta _c \leqslant \tfrac{3}{2}\pi \beta _c )$$ , these fixed points are globally stable. As a consequence we show that there is no screening of external charges for any activity if $$\beta 〉 \bar \beta _c $$ . Atβ c a supercritical bifurcation takes place and we investigate the behavior of the model forβ≲β c to show a weak form of screening.
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    Landscape ecology 3 (1989), S. 43-51 
    ISSN: 1572-9761
    Keywords: Czechoslovakia ; CSSR ; Slovakia ; ecological model ; planning ; landscape management ; stability ; disturbance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Development of the general ecological model (EM) of the CSSR has been included in the state program for environmental policy - the Ecoprogramme of the CSSR — at a scale of 1:1 000 000 for the entire Czechoslovak territory and at a scale of 1:500 000 for the Czech Socialist Republic (CSR) and the Slovak Socialist Republic (SSR). The objective of the first EM stage was to make a survey of spatial differentiation of the major ecological problems of the country. The EM consists of four parts, three analytical and one synthetic. These parts are: a. The ecological state (value) of the current spatial structure of the landscape. b. Ecological stress factors in the landscape. c. Protection of nature and natural resources. From the spatial synthesis of these three groups (from their spatial encounters), the following synthetic group of conditions was obtained: d. Regional ecological problems, a system of ecologically stable areas, environmental stress factors and factors endangering the ecological stability of the landscape, the natural resources and the human environment.
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    Acta mechanica solida Sinica 2 (1989), S. 285-294 
    ISSN: 0894-9166
    Keywords: Liapunov function ; stability ; discrete time system ; decision matrix
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The purpose of this paper is to present a new method for constructing Liapunov function and determining the stability of discrete time systems with a computer on the basis of the similarity transformation theory by directly applying the system matrix of the system under discussion instead of solving the discrete Liapunov's matrix equation.
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    Pure and applied geophysics 130 (1989), S. 743-749 
    ISSN: 1420-9136
    Keywords: Dynamic systems ; multiple equilibrium ; stability
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    Topics: Geosciences , Physics
    Notes: Abstract A set of ordinary differential equations describing a mechanical system subject to forcing and dissipation is considered. A topological argument is employed to show that if all time-dependent solutions of the governing equations are bounded, the equations admitN steady solutions, whereN is a positive odd integer and where at least (N−1)/2 of the steady solutions are unstable. The results are discussed in the context of atmospheric flows, and it is shown that truncated forms of the quasigeostrophic equations of dynamic meteorology and of Budyko-Sellers climate models satisfy the hypotheses of the theorem.
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    Acta applicandae mathematicae 4 (1985), S. 225-258 
    ISSN: 1572-9036
    Keywords: 92A15 ; Prey ; predator ; competition ; dynamical system ; ordinary differential equation ; phase diagram ; equilibrium ; trajectory ; stability ; bifurcation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We consider a problem of the dynamics of prey-predator populations suggested by the content of a letter of the biologist Umberto D'Ancona to Vito Volterra. The main feature of the problem is the special type of competition between predators of the same species as well as of different species. Two classes of cases are investigated: a first class in which the behaviour of the predator is ‘blind’ and the second one in which the behaviour is ‘intelligent’. A qualitative analysis of the dynamical systems under consideration is followed by a numerical analysis of the most significant cases.
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    Acta applicandae mathematicae 62 (2000), S. 23-130 
    ISSN: 1572-9036
    Keywords: stability ; functional equations ; Cauchy difference ; semigroup ; inequalities ; approximate
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    Topics: Mathematics
    Notes: Abstract In this paper, we study the stability of functional equations that has its origins with S. M. Ulam, who posed the fundamental problem 60 years ago and with D. H. Hyers, who gave the first significant partial solution in 1941. In particular, during the last two decades, the notion of stability of functional equations has evolved into an area of continuing research from both pure and applied viewpoints. Both classical results and current research are presented in a unified and self-contained fashion. In addition, related problems are investigated. Some of the applications deal with nonlinear equations in Banach spaces and complementarity theory.
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    International journal of fracture 105 (2000), S. 57-79 
    ISSN: 1573-2673
    Keywords: Interface toughness ; interface debonding ; stability ; adhesive interface ; bimaterial.
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper, we studied the interface debonding when a crack perpendicularly approaches an interface between two dissimilar elastic materials. An interface toughness law was first defined according to an adhesive model governing the interface fracture. By analysing the interaction between the normally approaching crack and the interface crack and by tacking account of the adhesive forces at ends of the interfacial crack, a model for studying the interface debonding and the debonding stability was established. It is observed that the interface debonding toughness depends strongly on the mixed mode locally produced over the plastic adhesive zone of the interface. Moreover, the interface debonding may be unstable, i.e. the interface debonding length may jump from an initial value to a certain final value under critical remote loading. This jump may be surprisedly important in certain cases. These results agree with the experimental works gathered so far and can be used to explain the mechanism of 'crack arrestor' formed by an interface.
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  • 44
    ISSN: 1573-4919
    Keywords: microtubules ; assembly/diassembly ; ATP ; cAMP ; phosphorylation ; stability
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    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The relevance of protein phosphorylation, transphosphorylation and binding phenomena in the kinetics of the ATP-induced assembly of cycle-purified microtubule protein from mammalian brain were studied. ATP was able to induce the polymerization of microtubules of normal appearance. However, the assembled structures, were unstable and microtubules depolymerized after achievement of a transitory maximum. Cyclic AMP reduced the amplitude of the polymerization maximum in a concentration-dependent manner, correlating with the stimulation of the endogenous phosphorylation reaction. When microtubule assembly was induced by GTP, in the presence of various concentrations of ATP, the slope of the depolymerization phase was found to depend on the concentration of ATP. Fluoride ion inhibited the endogenous phosphorylation reaction and reduced the disassembly rate, in a concentration-dependent manner. Evidence is also presented indicating that ATP did not bind to phosphocellulose-purified tubulin. These results further contribute to indicate that ATP and cyclic AMP, acting coordinately to control the phosphorylation extent of microtubule proteins are important factors to determine microtubule stability within the cell. Some implications of this mechanism for the regulation by cAMP of the initiation of DNA synthesis and mitosis are considered.
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  • 45
    ISSN: 1573-4943
    Keywords: Methanol dehydrogenase ; Ca2+ ; binding ; activity ; stability
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The effects of exogenously added Ca2+ on the enzymatic activity and structural stability of methanol dehydrogenase were studied for various Ca2+ concentrations. Methanol dehydrogenase activity increased significantly with increasing concentration of Ca2+, approaching saturation at 200 mM Ca2+. The effect of Ca2+ on the activation of MDH was time dependent and Ca2+ specific and was due to binding of the metal ions to the enzyme. Addition of increasing concentration of Ca2+ caused a decrease of the intrinsic tryptophan fluorescence intensity in a concentration-dependent manner to a minimum at 200 mM, but with no change in the fluorescence emission maximum wavelength or the CD spectra. The results revealed that the activation of methanol dehydrogenase by Ca2+ occurred concurrently with the conformational change. In addition, exogenously bound Ca2+ destabilized MDH. The potential biological significance of these results is discussed.
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    Journal of mathematical biology 21 (1985), S. 285-298 
    ISSN: 1432-1416
    Keywords: Population dynamics ; coexistence ; mutualism ; persistence ; predator-mediated coexistence ; stability
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    Topics: Biology , Mathematics
    Notes: Abstract We address the question of the long term coexistence of three interacting species whose dynamics are governed by the ordinary differential equations x i = X i f i (i = 1, 2, 3). In order for any theory in this area to be useful in practice, it must utilize as little information as possible concerning the forms of the f i , in view of the great difficulty of determining these experimentally. Here we obtain, under rather general conditions on the equations, a criterion for judging whether the species will coexist in a biologically realistic manner. This criterion depends only on the behaviour near the one or two species equilibria of the two dimensional subsystems, the behaviour there being relatively easy to examine experimentally. We show that with the exception of one class of cases, which is a generalization of a classical example of May and Leonard [21], invasibility at each such equilibrium suitably interpreted is both necessary and sufficient for a strong form of coexistence to hold. In the exceptional case, a single additional condition at the equilibria is enough to ensure coexistence.
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    Journal of mathematical biology 22 (1985), S. 81-104 
    ISSN: 1432-1416
    Keywords: FitzHugh-Nagumo equation ; pulse solution ; stability
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    Topics: Biology , Mathematics
    Notes: Abstract The FitzHugh-Nagumo equation u t =u xx +f(u)-w, u t =b(u-dw), is a simplified mathematical description of a nerve axon. If the parameters b〉0 and d⩾0 are taken suitably, this equation has two travelling pulse solutions with different propagation speeds. We study the stability of the fast pulse solution when b〉0 is sufficiently small. It is proved analytically by eigenvalue analysis that the fast pulse solution is “exponentially stable” if d〉0, and is “marginally stable” but not exponentially stable if d=0.
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    Acta mechanica Sinica 2 (1986), S. 193-205 
    ISSN: 1614-3116
    Keywords: stability ; neutral curve ; nonparallelism of the boundary layer flow ; quas-parallel flow
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The effect of the nonparallelism of the boundary layer flow over a flat plate on its stability characteristics has been investigated by several authors, and it was claimed that the results of the theoretical calculations are already in good agreement with the experimental observations. However, this is not true. In this paper, this problem is reinvestigated, using two different methods. It is found that within the framework of linear theory, the theoretical results are in fact not in good agreement with the experimental observations. To settle this problem, nonlinear effect must be taken into consideration.
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    Acta mechanica Sinica 3 (1987), S. 123-138 
    ISSN: 1614-3116
    Keywords: gravity flow with free surface ; complex variable function ; boundary-integral equation ; convergence ; stability ; estimation of error
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Gravity potential flows with free surface still present considerable difficulties in non-linear mathematical problems. Previous researchers using analytic function theory could consider only simple geometrical boundaries. Analyzing curvilinear solid boundaries by means of analytic theory is a difficult problem that has not been solved. In this paper, using Muskhelishvili's singular integral equation theory, we turn the gravity flow problem into the Riemann-Hilbert problem. Taking the length of the streamline of the boundary as the independent variable and the velocity potential of the boundary as the function to be determined, we avoid the difficulty that the angle of the curved fixed part is unknown. Following the difference method and the finite element method, we develop a new numerical method that is suitable for complex solid boundaries and overcome the difficulties encountered in applying analytic function theory. Under known discharge, the convergence and stability of the method have been proved and an estimation of error has been obtained. The method has been successfully applied to the calculation of the flow past spillway buckets. The calculated values agree well with the measured results.
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    Acta mechanica Sinica 5 (1989), S. 109-117 
    ISSN: 1614-3116
    Keywords: stability ; boundary layer ; compliant wall
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The stability characteristics of laminar boundary layers over compliant walls was studied by the linear theory. Unlike the previous authors, the coupled motion of the fluid and solid was required to satisfy the continuity conditions of both the velocity and stress at the interface. Results of calculations show that as the speed ratio or density ratio exceeds a certain threshold value, the two types of unstable waves will no longer be distinguishable, and the tangential component of the disturbance stress is no longer negligible. So the neglect of it, as the previous authors did, is unjustified.
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    Acta mechanica Sinica 16 (2000), S. 264-272 
    ISSN: 1614-3116
    Keywords: nonlinear dynamics ; bifurcation ; stability ; fluid-solid interaction
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract This paper studies interactions of pipe and fluid and deals with bifurcations of a cantilevered pipe conveying a steady fluid, clamped at one end and having a nozzle subjected to nonlinear constraints at the free end. Either the nozzle parameter or the flow velocity is taken as a variable parameter. The discrete equations of the system are obtained by the Ritz-Galerkin method. The static stability is studied by the Routh criteria. The method of averaging is employed to examine the analytical results and the chaotic motions. Three critical values are given. The first one makes the system lose the static stability by pitchfork bifurcation. The second one makes the system lose the dynamical stability by Hopf bifurcation. The third one makes the periodic motions of the system lose the stability by doubling-period bifurcation.
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    Acta mechanica Sinica 3 (1987), S. 297-303 
    ISSN: 1614-3116
    Keywords: three-dimensional unsteady gas flow ; difference scheme ; stability ; artificial viscosity
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The artificial viscosity method for three—dimensional unsteady gas flow is developed. The stability of finite difference scheme in this case is investigated. The necessary and sufficient conditions for the stability are obtained; these conditions formally agree with the two-dimensional result in Rusanov's paper.
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    Acta mechanica Sinica 3 (1987), S. 326-334 
    ISSN: 1614-3116
    Keywords: elastic curved bars ; bifurcation ; stability
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A general discussion about the stability of arbitrary elastic curved bars in space under combined actions of bending and twisting is given in this paper. A system of Eqs. (28)–(36) for perturbation functions near some equilibrium state is presented. With appropriate boundary conditions, the nontrivial solution corresponds to the critical state. Five examples are analysed in this paper. Some of them are new results and others are old problems treated using the new method.
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    Acta mechanica Sinica 3 (1987), S. 107-112 
    ISSN: 1614-3116
    Keywords: Casson fluid ; rotating disk ; film thickness ; stability
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The flow of a thin layer of a Casson fluid on a fast rotating disk is considered. The film thickness distribution at various times for various initial thickness distribution is calculated. The stability of the flow is examined.
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  • 55
    ISSN: 1573-5125
    Keywords: discharge effects on lotic invertebrates ; disturbance ; persistence ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Temporal and spatial trends were examined in benthic macroinvertebrate and physical-chemical data collected for at least ten years at ten sites along the plains reach of the Cache la Poudre River, Colorado, USA. A distinct longitudinal environment gradient was found as many of the water chemistry parameter levels changed downstream from the reference site. Seasonal Kendall analyses on individual sites indicated that several chemical parameters, including conductivity, un-ionized NH3-N and NO2-N have increased since the beginning of the study within most sites. Levels of some parameters (e.g., dissolved oxygen, un-ionized NH3-N) violated aquatic life standards a few times during the study. Over 175 taxa of macroinvertebrates (primarily insects) were collected in the study reach from 1981–1996. Results from detrended correspondence analyses (DCA) on macroinvertebrate data indicated that this stretch of the river exhibited little longitudinal change beyond the two farthest upstream sites. There was a decline in macroinvertebrate density and total number of taxa within most individual sites during 1983–1984, corresponding with the highest recorded discharge in 75 years (1983) and a prolonged, heavy spring runoff in 1984. Taxa richness and density recovered to pre-1983 levels within a few months to a year following the high flows at most sites. These findings suggested that the macroinvertebrate assemblages had low resistance to disturbance, but high resilience. However, the results from DCAs and Kendall's Coefficient of Concordance (W) on individual sites for the entire study period suggested a similar macroinvertebrate community structure through time. It would appear that the composition and abundance of the lotic macroinvertebrate assemblages in the Poudre River has remained relatively constant over the long-term. This has occurred even with some potentially negative changes in water chemistry and increased urban development.
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    Journal of mathematical chemistry 28 (2000), S. 325-340 
    ISSN: 1572-8897
    Keywords: numerical method ; stability ; Hopf bifurcation ; coupled oscillator
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    Topics: Chemistry and Pharmacology , Mathematics
    Notes: Abstract A second-order accurate numerical method has been proposed for the solution of a coupled non-linear oscillator featuring in chemical kinetics. Although implicit by construction, the method enables the solution of the model initial-value problem (IVP) to be computed explicitly. The second-order method is constructed by taking a linear combination of first-order methods. The stability analysis of the system suggests the existence of a Hopf bifurcation, which is confirmed by the numerical method. Both the critical point of the continuous system and the fixed point of the numerical method will be seen to have the same stability properties. The second-order method is more competitive in terms of numerical stability than some well-known standard methods (such as the Runge–Kutta methods of order two and four).
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    Aquatic ecology 23 (1989), S. 73-83 
    ISSN: 1573-5125
    Keywords: model ; fish ; vegetation ; eutrophication ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A simple mathematical model was constructed, describing the relationships between pike, bream, aquatic macrophytes and the nutrient loading of shallow lakes. The model is analyzed with the use of zero-isoclines. It is concluded that, over a certain range of nutrient concentrations, the ecological relations incorporated in the model can give rise to the existence of two alternative stable equilibria;viz. a turbid bream-dominated one, and a clear state in which pike and aquatic vegetation are abundant. Under oligotrophic conditions, the clear-water state represents the only stable equilibrium; however, at high nutrient levels, the clear state is absent, or only locally stable. The response of the model to both increase and decrease of the nutrient level is characterised by hysteresis. The results indicate that manipulation of fish densities as a measure to improve water quality is only likely to produce long-term results when the nutrient level is below a certain threshold.
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  • 58
    ISSN: 1573-8221
    Keywords: D-amino acid ; dipeptides ; stability ; integrative functions of the brain
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    Topics: Biology , Medicine
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  • 59
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    Chemistry of heterocyclic compounds 36 (2000), S. 115-133 
    ISSN: 1573-8353
    Keywords: thiophthalylium salts ; methods of preparation ; structure ; stability ; reactivity ; electrophilic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Methods of preparation, chemical reactions, the structures and reactivity of thiophthalylium ions are reviewed.
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  • 60
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    Journal of scientific computing 15 (2000), S. 441-456 
    ISSN: 1573-7691
    Keywords: modified conjugate gradient method ; conjugate gradient method ; Krylov space ; convergence rate ; stability
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    Topics: Computer Science
    Notes: Abstract We consider the modified conjugate gradient procedure for solving A $$\underline x $$ = $$\underline b $$ in which the approximation space is based upon the Krylov space associated with A 1/p and $$\underline b $$ , for any integer p. For the square-root MCG (p=2) we establish a sharpened bound for the error at each iteration via Chebyshev polynomials in $$\sqrt A$$ . We discuss the implications of the quickly accumulating effect of an error in $$\sqrt A$$ $$\underline b $$ in the initial stage, and find an error bound even in the presence of such accumulating errors. Although this accumulation of errors may limit the usefulness of this method when $$\sqrt A$$ $$\underline b $$ is unknown, it may still be successfully applied to a variety of small, “almost-SPD” problems, and can be used to jump-start the conjugate gradient method. Finally, we verify these theoretical results with numerical tests.
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    Neural processing letters 12 (2000), S. 129-144 
    ISSN: 1573-773X
    Keywords: associative memory ; dynamical systems ; Glauber dynamics ; Hopfield model ; infinite dimensional state space ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A generalization of the Little–Hopfield neural network model for associative memories is presented that considers the case of a continuum of processing units. The state space corresponds to an infinite dimensional euclidean space. A dynamics is proposed that minimizes an energy functional that is a natural extension of the discrete case. The case in which the synaptic weight operator is defined through the autocorrelation rule (Hebb rule) with orthogonal memories is analyzed. We also consider the case of memories that are not orthogonal. Finally, we discuss the generalization of the non deterministic, finite temperature dynamics.
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  • 62
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    Neuroscience and behavioral physiology 16 (1986), S. 333-339 
    ISSN: 1573-899X
    Keywords: adaptability ; stability ; electroencephalogram ; connectability of EEG components
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    Topics: Biology , Medicine
    Notes: Abstract The problem of the stability and adaptability of regulatory processes is considered, taking as a point of departure N. P. Bekhtereva's theory regarding stable pathological states, and inflexible and adaptable links in control systems. The need to introduce a probabilistic approach is emphasized. Generalizations are made on materials relating to the connectability of the separate components of the biorhythms of functional systems, and to the stability of their amplitude-frequency characteristics. The corpus of facts permitted the successful development in clinical practice of functional biocontrol and feedback.
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  • 63
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    Dynamics and control 10 (2000), S. 47-61 
    ISSN: 1573-8450
    Keywords: stability ; robust control ; Lyapunov approach ; discrete system
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Control design of nonlinear discrete-time uncertain systems with (possibly fast) uncertain parameters is considered. We study the effect of only partially compensating the uncertainty. The optimal choice of a design parameter, which indicates the amount of compensation, is recommended.
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    Dynamics and control 10 (2000), S. 255-276 
    ISSN: 1573-8450
    Keywords: continuous-time systems ; frequency weighted model reduction ; gradient flow ; optimization ; stability
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Inthis paper, a model reduction technique based on optimizationis presented. The objective function minimized is the impulseenergy of the overall system. An extension of the technique tothe frequency weighted case is also presented, where single-sidedor double-sided weightings can be incorporated in the reductionprocedure. The paper proposes an alternative to find an optimizationsolution by solving ordinary differential equations which aregradient flow associated with the objective function to be minimized.Two examples are presented to illustrate the effectiveness ofthe method.
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  • 65
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    Aquatic geochemistry 6 (2000), S. 1-17 
    ISSN: 1573-1421
    Keywords: lakes ; density ; compressibility ; expansibility ; conductivity ; stability ; pvt properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract In recent years, a number of workers have studied the stability of deep lakes such as Lake Tanganyika, Lake Baikal and Lake Malawi. In this paper, the methods that can be used to determine the effect that the components of lakes have on the equation of state are examined. The PVT properties of Lakes have been determined by using apparent molal volume data for the major ionic components of the lake. The estimated PVT properties (densities, expansibility and compressibilities) of the lakes are found to be in good agreement with the PVT properties (P) of seawater diluted to the same salinity. This is similar to earlier work that showed that the PVT properties of rivers and estuarine waters could also be estimated from the properties of seawater. The measured densities of Lake Tanganyika were found to be in good agreement (± 2 × 10-6 g cm-3) with the values estimated from partial molal properties and the values of seawater at the same total salinity (ST = 0.568‰). The increase in the densities of Lake Tanganyika waters increased due to changes in the composition of the waters. The measured increase in the measured density (45 × 10-6 g cm-3) is in good agreement (46 × 10-6 g cm-3) with the values calculated for the increase in Na+, HCO3 -, Mg2+, Ca2+ and Si(OH)4. Methods are described that can be used to determine the conductivity salinity of lakes using the equations developed for seawater. By combining these relationships with apparent molal volume data, one can relate the PVT properties of the lake to those of seawater.
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  • 66
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    Mechanics of composite materials 36 (2000), S. 475-480 
    ISSN: 1573-8922
    Keywords: stability ; three-dimensional theory ; tribotechnics ; elastoplastic deformations ; viscoelasticity ; surface ; tracking and dead loads ; laminated coating ; piecewise-homogeneous model ; active loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The problem of surface instability of laminated coatings with inelastic properties is considered within the framework of a model of piecewise-homogeneous media on the basis of the three-dimensional linearized theory of stability. A general statement of the problem is formulated and the basic characteristic equations are derived. The solutions of particular problems are obtained for elastoplastic and viscoelastic models of solids.
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  • 67
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    Journal of dynamical and control systems 6 (2000), S. 503-510 
    ISSN: 1573-8698
    Keywords: nonconservative mechanical systems ; stability ; Lyapunov functions ; attraction domain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Mechanical systems subjected to dissipative, gyroscopic, conservative, and also nonconservative positional forces are considered. The question of the effect of dissipative, gyroscopic, and conservative forces on the motion stability of a mechanical systems is determined by classical Kelvin–Chetaev theorems [1]. The presence of nonconservative positional forces considerably complicates the situation and excludes direct application of these theorems. Applying Lyapunov's functions method the condition of asymptotic stability of a mechanical system under the action of all listed above forces is obtained. Moreover, the estimation of the attraction domain in phase space is found. The precession system which is used in the solution of some problems in the applied theory of the gyroscopic systems is also examined. The connection between the stability of origin and precession systems is detected. Theoretical results are applied to the stabilization problem of stationary motion of the balanced gimbal suspension gyro by means of external moments.
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    Pharmaceutical research 4 (1987), S. 177-180 
    ISSN: 1573-904X
    Keywords: stability ; initial-rate method ; decomposition product ; stability-indicating assay
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The determination of potency or shelf life, impurity limit testing, and study of reaction mechanisms are considered as different aspects of drug stability. These aspects traditionally have been treated in isolation. The current criterion for a stability-indicating assay is criticized and the merits of choosing reactant or decomposition product for monitoring decomposition are discussed. The initial-rate method of determining reaction order and rate constants by analysis of decomposition product is described and its potential advantages over traditional integral methods are discussed. Examples of the application of the initial-rate method to simple and complex drug decomposition systems for the determination of decomposition rate constants are given. Applications to limit testing and study of reaction mechanisms are outlined and the dependence of the initial-rate method and decomposition product analysis on modern chromatographic methods is emphasized.
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  • 69
    ISSN: 1573-904X
    Keywords: phenobarbital ; stability ; solubility ; emulsions ; solutions ; elixirs ; high-performance liquid chromatographic (HPLC) analysis
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    Topics: Chemistry and Pharmacology
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  • 70
    ISSN: 1573-5060
    Keywords: Avena ; genetic correlation ; genotype-environmentinteraction ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In order to test if selection can improve a population's adaptation to diverse environments simultaneously, three cycles of recurrent selection based on grain yield in Iowa, Idaho, and Norway were practiced in an oat (Avena sativaL.) population developed from North American, Scandinavian, and wild species (A. sterilis L.) germplasm sources. Specific objectives were to determine if selection: increased mean yields across environments and within all environments; changed the genetic correlation of yields in different environments; and changed genetic variation for yield within the population. We evaluated 100 to 210 randomly-chosen families from each cycle of selection at three Iowa locations, in Idaho, and in Norway for two years. Grain yield within each location and mean yields across locations increased significantly over cycles of selection. Mean yields across locations expressed as a percent of the original population mean increased at a rate of 2.6% per year. Several families from the third cycle population exhibited both high mean yields across locations and consistently high yields within all locations. Average genetic correlations of yield in different environments were higher in the second cycle than in the original population. A trend of reduced genetic variation and heritability was observed in Iowa only. These results suggest that we successfully improved mean population yield both within and across locations, and yield stability across environments, and in developing families with outstanding adaptation to diverse environments.
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    Euphytica 36 (1987), S. 265-273 
    ISSN: 1573-5060
    Keywords: Hordeum vulgare ; barley ; dry areas ; stress-tolerance ; stability ; bulk method ; multilocation testing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Using the traditional approach (selection for grain yield) it has been found that F3 families derived from F2's selected under unfavourable conditions were more vigorous in the early stages of growth, taller, earlier in heading and with larger yields than F3 families derived from F2's selected under favourable conditions. A high and negative correlation coefficient was found between the drought susceptibility index and grain yield at the driest site, whereas at the wettest site the correlation coefficients were lower and in some cases positive, indicating the existence of traits which are desirable under drought and undesirable under favourable conditions, or vice versa. Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment. Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment.
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  • 72
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    Euphytica 35 (1986), S. 483-492 
    ISSN: 1573-5060
    Keywords: Triticum aestivum ; grain yield components ; stability ; development ; phenology ; differentiation ; heat resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Ten to 20 spring wheat (Triticum aestivum L.) cultivars of Israeli origin were grown in three winter (normal) and two summer (abnormal) growing seasons. During the period of emergence to anthesis mean daily temperature was on the average 12°C higher and photoperiod was about 3 h longer in the summer than in the winter. Data was collected on the durations of the periods from emergence to double-ridge (GS1), double ridge to anthesis (GS2) and anthesis to grain maturation (GS3), as well as on yield and yield components. The duration of all developmental stages was reduced by high temperature. While the duration of GS2 was the most thermo-sensitive, it may also have been reduced by the longer summer photoperiod. The effect of photoperiod on GS2 could not be isolated, but the results were interpreted to show that the effect of photoperiod on the duration of GS2 was relatively small. The most heat-affected yield component was number of grains per spikelet and the least affected component was the number of spikes per plant. High temperature reduced grain weight via reduced grain growth duration and not grain growth rate. A general linear regression model of yield on its components revealed that while variation for number of spikes per plant had the greatest effect on yield variation among cultivars in the winter, variation for number of grains per spikelet and spikelets per spike were by far the most important in the summer. Grain weight was the least important component, in this respect, in all seasons. Varieties which sustained the highest yield in hot environments were able to maintain the longest duration of GS2 and the highest number of grain per spike.
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  • 73
    ISSN: 1573-5060
    Keywords: Vigna radiata ; mungbean ; stability ; genotype-environment interaction ; wide adaptability ; AVRDC ; segmented regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Yield data from the 5th–12th international mungbean nursery (IMN) trials conducted at 23 sites in 15 countries were analyzed by conventional stability analysis—regression of genotype mean on the environmental index, and by segmented regression analysis—fitting separate linear regressions in low yielding and high yielding environments. The gene pool base concept allows comparison of genotypes from different IMN trials grown in different years and sites. A very high positive linear relationship was observed between the regression coefficient and the average yield of cultivars, indicating that high yielding cultivars were less stable across environments. When data points of the regression of genotype mean and site mean for VC 1973A, a high yielding and widely adapted cultivar, were examined, the relationship appeared not to be linear. The segmented regression analysis improved the coefficient of determination (r2) and the genotypes were grouped based on regression coefficients in high yielding and low yielding environments. Different categories of genotypes suitable for high input environments, widely adaptable genotypes, and highly stable genotypes were identified.
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    Hydrobiologia 161 (1988), S. 133-148 
    ISSN: 1573-5117
    Keywords: Ceratium spp ; nutrients ; stability ; long-term ; parasites of phytoplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Changes in the annual population densities of Ceratium spp. in three adjacent English lakes, Windermere, Esthwaite Water and Blelham Tarn, are summarised over the 41 year period 1945–1985. In these lakes the genus is represented by two species, C. hirundinella (O.F. Müll) Bergh. and C. furcoides (Levander) Langhans. Although the species have not been distinguished over the entire study period, they have been shown by examination of preserved samples to undergo marked changes of relative abundance in Esthwaite Water. Both long-term (years) and short-term (within year) changes of populations densities of Ceratium spp. are considered in relation to possible controlling factors including recruitment of the inoculum, nutrient enrichment, physical stability and fungal epidemics. Given an early inoculum, the relative success of Ceratium populations in these lakes decreases along gradients of increasing mixed depths, increasing turbulence and decreasing retention times. The potential for good population growth is regulated by energy inputs, lake bathymetry and hydraulic characteristics. The realisation of such growth is governed by nutrient availability and microbial grazing. The significance of large between-year differences of populations of Ceratium spp. for general lake metabolism is illustrated for summers of contrasting production in Esthwaite Water.
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    Hydrobiologia 142 (1986), S. 121-127 
    ISSN: 1573-5117
    Keywords: benthos ; stability ; density dependent mortality ; temperature ; organic enrichment ; North Sea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Biannual sampling (March and September) has been carried out over the period 1972 to 1985 at a muddy sand station, 55 m depth, with fauna belonging to the deeper offshore edge of Petersen's Amphiura filiformis community. During the period 1974 to 1980 the community exhibited a high degree of persistence stability. This stability was lost between 1980 and 1983, with rising total numbers and biomass and changes in species ranking. There is some evidence of a downward reversal between 1984–85. Evidence suggests that the principal stabilising process is density dependent mortality mediated by competition in a food limited environment. The principal destabilising process appears to be periodic fluctuations in the organic flux to the bottom. A secondary destabilising process is clearly concerned with fluctuating winter temperature. In competitive terms, cold winters favour increased survival in the dominant species at the expense of the lesser ranked species. This process is, however, more ephemeral and subject to adjustment within the time scale of a year.
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    Hydrobiologia 171 (1989), S. 159-170 
    ISSN: 1573-5117
    Keywords: Daphnia galeata mendotae ; Daphnidae ; Cladocera ; Crustacea ; cyclomorphosis ; phenotypic variability ; stability ; temperate lake ; coefficient of variation ; invertebrate predation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phenotypic change is studied in a cyclomorphicDaphnia galeata mendotae population known from previous studies to be clonally diverse. Morphological analyses revealed cyclical changes in both adult and juvenile helmet length and tailspine length which were: 1) strongly correlated with mean water temperature; and 2) repeated annually during the 3-year study period. Field populations exhibited high (5% to 30%) coefficients of variation (CV) for both helmet length and tailspine length; the CV also exhibited seasonal fluctuations such that it was lowest in late summer. The period of highestDaphnia helmet development coincides with peak densities of the common invertebrate predatorsChaoborus andLeptodora. The fluctuations in CV may be due to both differential phenotypic expression of the coexisting clones and invertebrate predation.
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  • 77
    ISSN: 1573-5117
    Keywords: thermal structure ; heat content ; stability ; annual cycle ; diel variation ; tropical lakes
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    Topics: Biology
    Notes: Abstract The thermal structure, heat content and stability were studied in Lakes Dom Helvécio and Carioca during an annual cycle. It was found that the maximum heat content, stability and work of the wind in Lake Dom Helvécio correspond to two, four and four times, respectively, the values for the Lake Carioca. These difference can be attributed to morphometric differences in the lakes. A long-term record of heat content and stability for lake Carioca is also presented. Diel variations were studied in summer and winter. The tropicality of the lakes is discussed and compared with other lacustrine systems.
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    Hydrobiologia 165 (1988), S. 115-128 
    ISSN: 1573-5117
    Keywords: heat budget ; stability ; saline lake ; Vestfold Hills ; Antarctica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Deep Lake, a hypersaline lake of about ten times seawater concentration, rarely freezes and is characterized by a monomictic thermal cycle, Winter circulation, at c. −17 °C, lasts for two to three months. In summer, epilimnetic temperatures from 7–11 °C result in large vertical thermal gradients (21–26 °C) which combine with the enhanced rate of density change per degree Celsius, accompanying such high salt concentration, to produce a particularly stable density configuration in Deep Lake (Schmidt stability c. 8000 g-cm cm−2; 0.785 J cm−2). The Birgean annual heat budget (c. 24500 cal cm−2; 102.7 103 J cm−2) is comparable to that of a temperate lake with a similar mean depth, despite the comparatively high ratio of Birgean wind work to annual heat budget (0.37 g-cm cal−1). Deep lake retains c. 50% of the incident solar radiation during the short summer heating period; within the range estimated for ‘first class’ lakes in North America. Extended daylight hours certainly contribute to the high maximum rate of heating in the lake (444 cal cm−2 day−1; 1.86 103 J cm−2 day−1). Deep Lake cools at a rate less than half its average heating rate. Partitioning the total stability into thermal and saline components shows that salinity can contribute up to c. 20% of the maximum summer Schmidt stability. In early summer, the effect of small melt-streams is to increase stability by diluting the epilimnion. In autumn, evaporative water loss can overtake this effect, creating small de-stabilizing salinity gradients. The usually short-term stabilizing influence of snowfall and drift is less predictable, but is probably more common in winter when strong winds are most frequent. Hypersalinity has a profound effect on the physical cycle of Deep Lake, through freezing point depression and the increased rate of density change with temperature. These changes affect the lake's biota, both in relation to osmotic stress, and by effectively exposing them to a more thermally extreme environment. A comparison between Deep Lake and a smaller lake of similar salinity (Lake Hunazoko, Skarvs Nes), demonstrates that it is inappropriate to consider the biological effects of salinity in isolation. The smaller lake offers warmer epilimnetic conditions for at least part of the summer, which may explain the much greater limnetic algal production in Lake Hunazoko.
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  • 79
    ISSN: 1573-5168
    Keywords: amberjack ; myosin heavy chain ; cDNA ; α-helix ; coiled coils ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The structural stability of fish myosin depends upon species and temperatures of water in which fish live. Primary, secondary, and quaternary structures of myosin heavy chain (MyHC) from three species of fish living at different temperature ranges have been compared with those of rabbit MyHC in order to investigate the differences in stability. Primary structure of MyHC, although being accessible for warm-water and cold-water fish (carp and walleye pollack), was not available in previous for tropical-water fish literature; so in this study primary structure of MyHC of the tropical-water fish amberjack has been determined by cloning and sequencing its cDNA. The MyHC has 1938 amino acid residues (AA), which are almost as much as as those of carp and walleye pollack. The amberjack MyHC is 91–95% homologous with other fish and rabbit MyHCs. There is a discernible difference between animal species with stable myosin rod (amberjack, carp, and rabbit) and walleye pollack with unstable rod. Stable rod species have a high probability of forming coiled-coil around the COOH-terminal end of the rod, while the pollack has a low coiled-coil formation probability. In addition, the average scores of the coiled-coil for myosin rod were rabbit (1.738) 〉 amberjack (1.691) 〉 carp (1.680) 〉 walleye pollack (1.674) which correlated exactly with the observed stability. The results suggest that coiled-coil forming ability, particularly around the COOH-terminal end, directs structural stability of fish myosin rod.
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    Geotechnical and geological engineering 6 (1988), S. 195-214 
    ISSN: 1573-1529
    Keywords: Room and pillar mining ; yield pillars ; rock mechanics ; stability ; evaporites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary Significant increases in extraction ratio on the order of 6 to 8%, equivalent to as much as 142 t/m of panel advance, have occurred at the Big Island Mine during the last five years with the help of a practical rock mechanics program. This increase in resource recovery has also contributed to improvements in productivity. Both conventional and continuous machine mining have been used to mine two flat-laying trona beds at depths of 250 and 260 m in the Green River Formation in southwestern Wyoming. Conventional room and pillar mining originally was conducted in panels with extraction ratios of 58 to 60%. The use of yield pillars has allowed the panel extraction to increase to 66%. Continuous machine mining was introduced recently, with a 64% extraction ratio using long, narrow pillars and wide rooms. Further improvements in resource recovery seem feasible in the light of present mining experience. The rock mechanics program consisted of field instrumentation to determine the pillar and roof response to mining, and computer modelling to evaluate and help determine the stability of various layouts, which were then adopted for mining.
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    Multidimensional systems and signal processing 11 (2000), S. 109-124 
    ISSN: 1573-0824
    Keywords: 2-D linear systems ; optimal control ; stability ; unit memory linear repetitive processes ; numerical methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Because many optimal control problems require solution using iterative procedures they fall naturally in the realm of 2-D systems where the two dimensions are response time horizon and iteration index, respectively. The paper uses this observation to employ 2-D systems theory, in the form of unit memory repetitive process techniques, to analyse local stability and convergence behaviour of a continuous optimal control algorithm based on dynamic system optimisation and parameter estimation. Existing work is extended to incorporate unmatched terminal constraints. Necessary and sufficient conditions for stability are obtained whose evaluation require the solution of a difficult eigenvalue problem. The paper shows how solutions can be achieved using numerical and graphical facilities of MATLAB.
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    Multidimensional systems and signal processing 11 (2000), S. 339-358 
    ISSN: 1573-0824
    Keywords: 2-D systems ; descriptor systems ; singular systems ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we discussthe jump behavior and stability problems for 2-D linear shift-invariantsingular systems under the standard boundary conditions. It isshown that once a boundary condition or the input is inadmissiblein the classical sense, a group of non-causal or backward jumpsof the system states will be incited. This interpretation releasesthe conventional admissibility constraints on the boundary conditionsand inputs. Based on this observation, a systematic stabilitytheory is developed for 2-D singular systems. The well-knownbasic stability theorem for the 1-D singular systems or 2-D regularsystems is thus extended to the 2-D singular case.
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    Rheologica acta 28 (1989), S. 504-510 
    ISSN: 1435-1528
    Keywords: Taylor-Couette flow ; stability ; Doi-Edwards equation ; inertia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The stability of Taylor-Couette flow of entangled polymeric solutions to small axisymmetric stationary disturbances is analyzed using the Doi-Edwards constitutive equation in the small gap limit. A previous analysis of Karlsson, Sokolov, and Tanner for the general K-BKZ equation, of which the Doi-Edwards equation is a special case, reduces the problem to one of numerically evaluating seven viscoelastic functions of the shear rate $$\dot \gamma$$ in the gap. Of these seven, only three — two of which are related to the second normal stress difference, and one of them to shear thinning — significantly affect the flow stability. The negative second normal stress difference of the Doi-Edwards fluid stabilizes the flow at low values of the Weissenberg number λ1 $$\dot \gamma$$ , while shear thinning produces strong destabilization at moderate Weissenberg number. Hereλ 1 is the longest relaxation time. Non-monotonic effects of viscoelasticity on Taylor-Couette stability analogous to those predicted here have been observed in experiments of Giesekus. The extreme shear thinning of the Doi-Edwards fluid is also predicted to produce a large growth in the height of the Taylor cells, a phenomenon that has been seen experimentally by Beavers and Joseph.
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  • 84
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    Rheologica acta 24 (1985), S. 551-555 
    ISSN: 1435-1528
    Keywords: Torsional flow ; Oldroyd-B fluid ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract It is shown that the exact solution of the torsional flow of a class of Oldroyd-type fluids is kinematically similar to that for a Newtonian fluid. Furthermore, it is shown by a linearized stability analysis and by numerical integration, that the basic flow is unstable at high Weissenberg numbers. An Oldroyd fluid which has a negative second-normal stress coefficient is found to be more stable than one with zero (or positive) second-normal stress coefficient in this flow.
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  • 85
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    Rheologica acta 24 (1985), S. 321-322 
    ISSN: 1435-1528
    Keywords: Viscometric flow ; stability ; short memory approximation ; change of type ; upper convected Maxwell model
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    Topics: Chemistry and Pharmacology , Physics
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  • 86
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    Rheologica acta 28 (1989), S. 499-503 
    ISSN: 1435-1528
    Keywords: Taylor-Couetteflow ; stability ; Boger fluid ; Oldroyd-B equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Experimental evidence of a non-inertial, cellular instability in the Taylor-Couette flow of a viscoelastic fluid is presented. A linear stability analysis for an Oldroyd-B fluid, which is successful in describing many features of the experimental fluid, predicts the critical Deborah number,De c , at which the instability is observed. The dependence ofDe c on the value of the dimensionless gap between the cylinders is also determined.
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  • 87
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    Rheologica acta 27 (1988), S. 44-51 
    ISSN: 1435-1528
    Keywords: Polyelectrolytegel ; phase transition ; stability ; swelling ; collapse
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Swelling and collapse of a polyelectrolyte are shown to be the result of a delicate balance of three “thermodynamic forces”, viz. osmotic pressure, polymer elasticity, and van der Waals attraction. The behaviour of the polyelectrolyte gel is studied under isotropic pressure and under uniaxial and biaxial loading.
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  • 88
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    Rheologica acta 24 (1985), S. 469-473 
    ISSN: 1435-1528
    Keywords: Liquid crystal ; nematic ; semigroup ; stability ; tumbled state
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In shear flow of a nematic liquid crystal withα 3 ≧ 0 flow alignment cannot occur. The stability of the stationary in-plane solution, “the tumbled state”, is investigated using abstract techniques. Employing the existence of an elastic energy a sufficient criterion for stability is formulated. This criterion depends on the in-plane solution which is obtainable as a quadrature that is non-elementary except in special cases. It is shown that the tumbled state is stable and asymptotically stable for some physical configurations. The criterion presented is not a necessary condition for stability and thus only gives a lower bound.
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  • 89
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    Acta applicandae mathematicae 14 (1989), S. 125-133 
    ISSN: 1572-9036
    Keywords: 92A07 ; stationary solution ; immune response ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Some results connected with a simple mathematical model of infectious disease are discussed in order to demonstrate the approach to the modelling of such real processes. A more complicated model of antiviral immune response is presented. A new modification of this model in which targets for the viruses are immunocompetent cells is suggested.
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  • 90
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    Acta applicandae mathematicae 15 (1989), S. 211-234 
    ISSN: 1572-9036
    Keywords: 70F99 ; 70K20 ; 73C02 ; 35P30 ; Flexible body ; Lagrangian and Hamiltonian dynamics ; stability ; partial differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We analyse here the equations of motion of a planar body consisting of a rigid body with attached flexible rod. These equations take the form of coupled ordinary and partial differential equations. We analyse the equations both with and without centrifugal stiffening effects. Using the ‘energy-momentum’ method, we analyse nonlinear stability of the equilibria in each case. We also analyse the Hamiltonian and Poisson bracket structure of the system as well as the energy-momentum map and associated relative equilibria.
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  • 91
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    Journal of fusion energy 6 (1987), S. 275-279 
    ISSN: 1572-9591
    Keywords: Fusion cycles ; stochastic differential equations ; parametric noise ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The statistical properties of the (n)-Li-(T)-D-(n) fusion cycle response are examined via the general Fokker-Planck theory for linear systems with random coefficients. The Fokker-Planck equation for the chain carrier density probability distribution is obtained for a Gaussian stationary random reactivity fluctuation and the first few moment equations are used to establish the stability conditions of the mean and mean square. Finally, an expression for the spectral density of the chain carrier response is presented.
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  • 92
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    Journal of statistical physics 44 (1986), S. 907-920 
    ISSN: 1572-9613
    Keywords: Nonlinear equation ; stochastic process ; stability ; steady-state ; Gaussian closure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The anharmonic oscillator under combined sinusoidal and white noise excitation is studied using the Gaussian closure approximation. The mean response and the steady-state variance of the system is obtained by the WKBJ approximation and also by the Fokker-Planck equation. The multiple steadystate solutions are obtained and their stability analysis is presented. Numerical results are obtained for a particular set of system parameters. The theoretical results are compared with a digital simulation study to bring out the usefulness of the present approximate theory.
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  • 93
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    Journal of statistical physics 56 (1989), S. 533-545 
    ISSN: 1572-9613
    Keywords: Immune system ; dormant B cells ; cycles ; Jerne theory ; memory ; nonlinear phenomena ; stability
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    Topics: Physics
    Notes: Abstract The role of dormant B cells and cycles is analyzed in the context of a Lotka-Volterra network. It is shown that dormant B cells stabilize a cycle and that in this way both cooperate to preserve the internal image (memory) of an antigen. The network is embedded in a hierarchical scheme which allows adaptation, learning, and innovation by biased and random mutation.
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  • 94
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    Human ecology 15 (1987), S. 317-338 
    ISSN: 1572-9915
    Keywords: productivity ; diversity ; stability ; maintenance costs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Ethnic Sciences
    Notes: Abstract By describing the ecological implications of Mormon settlement in the Little Colorado River Basin, the paper demonstrates: (1) the application of general ecological concepts in human ecology, (2) the ecological basis for the evolution of complex human communities, (3) the interactive, hierarchical relationship between community diversity and environmental stability, and (4) the positive contribution that human ecology can make to the general discussion of diversity and stability in ecological systems. The paper gives a brief description of Mormon colonization in the Little Colorado River Basin. Local differences in community development are then related to environmental variation within the basin and compared to general ecological research expectations. The implications of community development in this region for explaining the relationship between diversity and stability in ecological systems are discussed.
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  • 95
    ISSN: 1572-9915
    Keywords: human ecology ; success ; seasonality ; intensification ; rural development ; diversity ; stability ; flexibility ; duck farming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Ethnic Sciences
    Notes: Abstract The success of an agricultural industry in commercial duck egg production in the swamplands of South Kalimantan (Borneo) is examined through the utilization of a human ecology framework. Seasonality of resource availability and human population growth are identified as two major constraints to production faced by farmers. Population increases in the urban sectors of southeastern Borneo also present economic opportunities for farmers because of the growing demand for poultry products. Farmers have responded by developing an intensification strategy in egg production based on the use of diversified resources for duck feed. The long-term consequences of these and other innovations in duck farming are discussed; and diversity-stability theory is examined for its applicability to this case of agricultural development and for rural development theory and practice.
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  • 96
    ISSN: 1573-5060
    Keywords: chile ; double haploid ; pepper ; pungency ; stability ; within-genotype variance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The response, in terms of capsaicinoid content, of chile (Capsicum annuum L.) genotypes to different environments was studied. Double haploidlines, an F1 hybrid, and an open-pollinated cultivar estimated the genotype, environment, and genotype-by-environment interaction effect on the total capsaicinoids and on individual capsaicinoids. Significant differences were observed among the genotypes and among genotype-by-environment interactions over the environments. Among the genotypes in an environment, the within-genotype variances were also significantly different. The double haploid line, HDA 207, had low within-genotype variance for individual and total capsaicinoids, with the exception of the isomer of dihydrocapsaicin. Also for HDA 270, the genotype-by-environment interaction was negligible for individual and total capsaicinoids, Indicating stability across environments.
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  • 97
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    Journal of optimization theory and applications 57 (1988), S. 265-293 
    ISSN: 1573-2878
    Keywords: Discrete-time systems ; infinite-horizon optimal control ; moving-horizon control ; state-control constraints ; nonquadratic cost functions ; stability
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    Topics: Mathematics
    Notes: Abstract Stability results are given for a class of feedback systems arising from the regulation of time-varying discrete-time systems using optimal infinite-horizon and moving-horizon feedback laws. The class is characterized by joint constraints on the state and the control, a general nonlinear cost function and nonlinear equations of motion possessing two special properties. It is shown that weak conditions on the cost function and the constraints are sufficient to guarantee uniform asymptotic stability of both the optimal infinite-horizon and moving-horizon feedback systems. The infinite-horizon cost associated with the moving-horizon feedback law approaches the optimal infinite-horizon cost as the moving horizon is extended.
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  • 98
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    Mathematical methods of operations research 29 (1985), S. 65-104 
    ISSN: 1432-5217
    Keywords: Additive cost criterion ; analytic behaviour of strategies ; ES strategy ; list schedule ; MES strategy ; priority rule ; quasi-stability ; regular measure of performance ; scheduling problems ; set strategy ; shift property ; stability ; stochastic scheduling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract The paper introduces the finite class of set strategies for stochastic scheduling problems. It is shown that the knownstable classes of strategies such as ES and MES strategies are of this type, as arelist-scheduling strategies such as LEPT and SEPT and other, more complicatedpriority-type strategies. Roughly speaking, set strategies are characterized by the fact that the decision as to which jobs should be started at timet depends only on the knowledge of the two sets of jobs finished up to timet and being processed at timet. Contrary to list scheduling strategies, set strategies may involve deliberate idleness of machines, i.e. may not be greedy and can therefore not generally be induced by priority rules. It is demonstrated that set strategies have useful properties. They are e.g.λ n -almost everywhere continuous and therefore show satisfactorystability behaviour w.r.t. weak convergence of the joint distribution of job durations. Furthermore, the optimum w.r.t.all strategies is already attained on this class if job durations are independent and exponentially distributed and the performance measure fulfills a certainshift condition. This shift property is a quite natural concept and generalizes aspects of the notion ofadditivity in semi-Markov decision theory and stochastic dynamic optimization. Its complete analytical characterization is a major object of this paper. Typical additive cost criteria such as makespan and flowtime are of course covered, which yields simultaneously a first step towards generalization of optimality of LEPT and SEPT rules, as known for special cases. In fact, in view of the obtained optimality result, the question of when deliberate idleness of machines can be avoided, gains considerable interest, as it characterizes stochastic environments in whichpriority strategies are optimal. This provides a major link with current research on the analysis of networks of queues in the context of computer systems.
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  • 99
    ISSN: 1573-0646
    Keywords: 2,5-diaziridinyl-3,6-bis(2-hydroxyethylamino)-1,4-benzoquinone ; BZQ ; light-sensitive ; solution ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The stability of the potential antitumour agent 2,5-diaziridinyl-3,6-bis(2-hydroxyethylamino)-1,4-benzoquinone (BZQ; NSC 224070) has been investgated by high-performance liquid chromatography. At 22°C in 0.05M buffer, BZQ was most stable at pH 9 with an apparent first-order rate constant (k) of about 0.014 h−11. There was reduced stability at pH values above and below 9.0. At a pH of 3 and 12 the values of k were 38 and 0.3 h−1, respectively. Stability of BZQ was adversely affected by increased temperatures (above 0°C), increased buffer concentration and light. Solutions of BZQ could not be frozen for any length of time, as the drug precipitated out in a form that would not redissolve (possibly a polymer). For parenteral administration to patients, it is suggested that BZQ would be most stable in 1.26% sodium bicarbonate solution when at room temperature, under normal laboratory lighting, 5% of the drug degraded (t0.95) in 5.5 h. Increased stability is obtainable in this medium by refrigeration and vigorous exclusion of light. Long term (24 h) infusions of BZQ could be considered in hypotonic sodium bicarbonate (30 mM) with careful exclusion of light as long as the volume of the infusion was small, e.g. 1 ml/h. Under these conditions to.95 was 42 h at 21.5°C.
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  • 100
    ISSN: 1573-0778
    Keywords: CHO cells ; gel microdrops ; human antibody ; population parameters ; productivity ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The long-term stability of high-level expression is the mostimportant factor to consider when choosing cell lines for the expression of recombinant proteins. Declining volumetricyields in large-scale fermentation can be caused by changes affecting the cell population as a whole such as loss in viability, depletion of nutrients or accumulation of metabolites affecting cell growth. Alternatively, geneticinstability may lead to the outgrowth of a less productive,metabolically favored sub-population. Currently a variety ofparameters are measured to monitor the condition of cells infermenters including glucose uptake, lactate accumulation andoxygen consumption; in addition, periodic viable cell countsallow the determination of the growth rate and viability of the population. All of these methods measure the condition ofthe cell population as a whole and changes must involve a significantly large proportion of the total culture in orderto be detectable. Here we report on a method that allows theevaluation of the productivity of individual cells. Using the gel microdrop secretion assay, we detected the appearance ofa sub-population of cells with lower productivity. Subsequentanalysis of the culture confirmed the existence of lower productivity cells with a lower vector copy number. Therefore,the single cell secretion assay proved to be a rapid method todetect and isolate a low productivity variant of the producer cell line.
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