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  • 1994  (50)
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  • Springer  (50)
  • American Institute of Physics (AIP)
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  • 1990-1994  (50)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    OR spectrum 16 (1994), S. 47-52 
    ISSN: 1436-6304
    Keywords: Vector optimization ; approximately efficient solutions ; stability ; Vektoroptimierung ; Näherungslösungen ; Stabilität
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Wir führen ein Konzept für Näherungslösungen in der Vektoroptimierung ein und vergleichen dieses mit einem neuen Konzept aus [8]. Weiterhin untersuchen wir Beziehungen zwischen der Menge der Näherungslösungen eines Vektoroptimierungsproblems und den Näherungslösungen eines entsprechenden parametrischen Ersatzproblems. Schließlich beweisen wir Stabilitätseigenschaften des skalaren Ersatzproblems.
    Notes: Abstract We introduce a concept for approximately efficient solutions in vector optimization and compare it with another recent concept given in [8]. Further, we study relations between the set of approximately efficient solutions of a vector optimization problem and the approximate solutions of a corresponding parametric surrogate optimization problem. Finally, we prove stability properties for the scalar surrogate problem.
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  • 2
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    Journal of dynamics and differential equations 6 (1994), S. 37-51 
    ISSN: 1572-9222
    Keywords: Celestial mechanics ; relative equilibria ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A criterion for the linear stability of relative equilibria of the Newtoniann-body problem is found in the case whenn−1 of the masses are small. Several stable periodic orbits of the problem are presented as examples.
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  • 3
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    Queueing systems 15 (1994), S. 279-288 
    ISSN: 1572-9443
    Keywords: Sample-path ; point processes ; workload ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this paper, by exploiting recent results on the pathwise behavior of the workload process in single server, work conserving queues of theG/G/1/∞ type, we show that the workload of multiserver, work conserving queues ofG/G/m/∞ (m〈∞) (andG/G/∞) queues satisfies an o(t) growth condition, provided that the time average of the work brought into the system is less thanm form 〈 ∞ (and finite form=∞).
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  • 4
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    Queueing systems 16 (1994), S. 115-137 
    ISSN: 1572-9443
    Keywords: Polling systems ; stability ; stochastic continuity ; general arrival process ; functional limit theorems.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The stability of a polling system with exhaustive service and a finite number of users, each with infinite buffers is considered. The arrival process is more general than a Poisson process and the system is not slotted. Stochastic continuity of the stationary distributions, rates of convergence and functional limit theorems for the queue length and waiting time processes have also been proved. The results extend to the gated service discipline.
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  • 5
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    Celestial mechanics and dynamical astronomy 58 (1994), S. 203-213 
    ISSN: 1572-9478
    Keywords: libration points ; resonances ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The stability of the triangular libration points in the case when the first and the second order resonances appear was investigated. It was proved that the first order resonances do not cause instability. The second order resonances may lead to instability. Domains of the instability in the two-dimensional parameter space were determined.
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  • 6
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    Journal of dynamics and differential equations 6 (1994), S. 639-658 
    ISSN: 1572-9222
    Keywords: Symmetry ; parabolic equations ; positive solutions ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Symmetry properties of positive solutions of a Dirichlet problem for a strongly nonlinear parabolic partial differential equation in a symmetric domainD ⊂ R n are considered. It is assumed that the domainD and the equation are invariant with respect to a group {Q} of transformations ofD. In examples {Q} consists of reflections or rotations. The main result of the paper is the theorem which states that any compact inC(D) negatively invariant set which consists of positive functions consists ofQ-symmetric functions. Examples of negatively invariant sets are (in autonomous case) equilibrium points, omega-limit sets, alpha-limit sets, unstable sets of invariant sets, and global attractors. Application of the main theorem to equilibrium points gives the Gidas-Ni-Nirenberg theorem. Applying the theorem to omega-limit sets, we obtain the asymptotical symmetrization property. That means that a bounded solutionu(t) asr→∞ approaches subspace of symmetric functions. One more result concerns properties of eigenfunctions of linearizations of the equations at positive equilibrium points. It is proved that all unstable eigenfunctions are symmetric.
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  • 7
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    Queueing systems 15 (1994), S. 211-238 
    ISSN: 1572-9443
    Keywords: polling system ; stability ; Markov chain ; stochastic monotonicity ; heavy traffic ; nonpreemptive local priority
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper deals with the stability of periodic polling models with a mixture of service policies. Customers arrive according to independent Poisson processes. The service times and the switchover times are independent with general distributions. The necessary and sufficient condition for the stability of such polling systems is established. The proof is based on the stochastic monotonicity of the state process at the polling instants. The stability of only a subset of the queues is also analyzed and, in case of heavy traffic, the order of explosion of the queues is given. The results are valid for a model with set-up times, and also when there is a local priority rule at the queues.
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  • 8
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    Queueing systems 17 (1994), S. 317-345 
    ISSN: 1572-9443
    Keywords: Single-server queue ; spatially distributed arrival points ; travelling server ; Brownian motion ; embedded Markov chain ; stability ; Tweedie's lemma ; regenerative processes ; stochastic decomposition ; equilibrium equations ; mean queue length
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Consider a queueing system where customers arrive at a circle according to a homogeneous Poisson process. After choosing their positions on the circle, according to a uniform distribution, they wait for a single server who travels on the circle. The server's movement is modelled by a Brownian motion with drift. Whenever the server encounters a customer, he stops and serves this customer. The service times are independent, but arbitrarily distributed. The model generalizes the continuous cyclic polling system (the diffusion coefficient of the Brownian motion is zero in this case) and can be interpreted as a continuous version of a Markov polling system. Using Tweedie's lemma for positive recurrence of Markov chains with general state space, we show that the system is stable if and only if the traffic intensity is less than one. Moreover, we derive a stochastic decomposition result which leads to equilibrium equations for the stationary configuration of customers on the circle. Steady-state performance characteristics are determined, in particular the expected number of customers in the system as seen by a travelling server and at an arbitrary point in time.
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  • 9
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    Celestial mechanics and dynamical astronomy 59 (1994), S. 345-374 
    ISSN: 1572-9478
    Keywords: Lagrangian points ; stability ; oblate primary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The non-linear stability of the libration pointL 4 in the restricted problem has been studied when there are perturbations in the potentials between the bodies. It is seen that the pointL 4 is stable for all mass ratios in the range of linear stability except for three mass ratios depending upon the perturbing functions. The theory is applied to the following four cases: (i) There are no perturbations in the potentials (classical problem). (ii) Only the bigger primary is an oblate spheroid whose axis of symmetry is perpendicular to the plane of relative motion (circular) of the primaries. (iii) Both the primaries are oblate spheroids whose axes of symmetry are perpendicular to the plane of relative motion (circular) of the primaries. (iv) The primaries are spherical in shape and the bigger is a source of radiation.
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  • 10
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    Journal of dynamics and differential equations 6 (1994), S. 447-486 
    ISSN: 1572-9222
    Keywords: Free boundary problems ; gasless combustion ; stability ; Hopf bifurcation ; 35R35 ; 35B40 ; 80A25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we analyze a simple free boundary model associated with solid combustion and some phase transition processes. There is strong evidence that this “one-phase” model captures all major features of dynamical behavior of more realistic (and complicated) combustion and phase transition models. The principal results concern the dynamical behavior of the model as a bifurcation parameter (which is related to the activation energy in the case of combustion) varies. We prove that the basic uniform front propagation is asymptotically stable against perturbations for the bifurcation parameter above the instability threshold and that a Hopf bifurcation takes place at the threshold value. Results of numerical simulations are presented which confirm that both supercritical and subcritical Hofp bifurcation may occur for physically reasonable nonlinear kinetic functions.
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  • 11
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    Journal of dynamics and differential equations 6 (1994), S. 325-334 
    ISSN: 1572-9222
    Keywords: Nonlinear Schrödinger equations ; anisotropic standing waves ; stability ; concentration compactness principle ; Davey-Stewartson system ; 35Q35 ; 35B35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study the stability of standing waves for a nonlinear Schrödinger equation, which derives from the generalized Davey-Stewartson system in the elliptic-elliptic case. We prove the existence of stable standing waves under certain conditions.
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  • 12
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    Journal of dynamics and differential equations 6 (1994), S. 631-637 
    ISSN: 1572-9222
    Keywords: stability ; fixed point index ; periodic solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we prove that a stable isolated fixed point of an orientation preserving local homeomorphism onR 2 has fixed point index 1. We also give a number of applications to differential equations. In particular, we deduce that a number of existence methods for producing periodic solutions of differential equations in the plane always produce unstable solutions.
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  • 13
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    Celestial mechanics and dynamical astronomy 60 (1994), S. 307-315 
    ISSN: 1572-9478
    Keywords: Asteroid ; libration ; resonance ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is known that an abridged case of the averaged planar general three-body problem, at first-order resonance, is analytically integrated, using an expansion of the disturbing function linear in the eccentricities. There exist different methods with the help of which the integration can be performed. For the first time Sessin and Ferraz-Mello in the years 1981–88 (Sessin, 1981, 1983; Ferraz-Mello and Sessin, 1984; Ferraz-Mello, 1987, 1988) did an analytic integration for the restricted elliptic three-body problem, in terms of the variablesK andH (K=ΣD j e j cos (ψ1−π j ),H=ΣD j e j sin (ψ1−π j ),D j = const, wheree j and π j are, respectively, the eccentricity and the longitude of the periapsis of thei-th planet, ψ1 is the Delaunay's anomaly), which is inconvenient for the analytical investigation of the evolution of the major semi-axesa j , the eccentricitiese j and the resonance phases ϕ j =ψ1−π j . Later, a different method for the analytical integration of the general three-body problem, in the variablesa j ,e j and ϕ j , was considered by the author (Shinkin, 1993). A disadvantage of both methods is the fact that they use non-canonical changes of variables. But there exists a third very beautiful canonical method of analytical integration of the general planetary problem, which is briefly considered in the present paper and allows us to describe the bifurcations of separatrices (i.e. appearance, disappearance, splitting and confluence of separatrices) separating the domains of libration and circulation of the resonance phase on the phase plane in the averaged planar general three-body problem at first-order resonance. The bifurcation parameter is analytically found and plays an important role in a qualitative description of all kinds of motion in the examined problem.
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  • 14
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    Acta applicandae mathematicae 37 (1994), S. 129-136 
    ISSN: 1572-9036
    Keywords: 35B35 ; 35Q30 ; 76N10 ; stability ; Navier-Stokes equations ; compressible fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We prove that the uniform stability at permanently acting disturbances of a given solution of the Navier-Stokes equations for viscous compressible isothermic fluid is a consequence of the uniform exponential stability of the zero solution of so-called linearized equations.
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  • 15
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    Celestial mechanics and dynamical astronomy 60 (1994), S. 249-271 
    ISSN: 1572-9478
    Keywords: Chaos ; periodic orbits ; stability ; asymptotic curves ; homoclinic points ; heteroclinic points
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the structure of chaos in a simple Hamiltonian system that does no have an escape energy. This system has 5 main periodic orbits that are represented on the surface of section $$(y,\dot y)$$ by the points (1)O(0,0), (2)C 1,C 2(±y c, 0), (3)B 1,B 2(O,±1) and (4) the boundary $$y^2 + \dot y^2 = 1$$ . The periodic orbits (1) and (4) have infinite transitions from stability (S) to instability (U) and vice-versa; the transition values of ε are given by simple approximate formulae. At every transitionS →U a set of 4 asymptotic curves is formed atO. For larger ε the size and the oscillations of these curves grow until they destroy the closed invariant curves that surroundO, and they intersect the asymptotic curves of the orbitsC 1,C 2 at infinite heteroclinic points. At every transitionU →S these asymptotic curves are duplicated and they start at two unstable invariant points bifurcating fromO. At the transition itself the asymptotic curves fromO are tangent to each other. The areas of the lobes fromO increase with ε; these lobes increase even afterO becomes stable again. The asymptotic curves of the unstable periodic orbits follow certain rules. Whenever there are heteroclinic points the asymptotic curves of one unstable orbit approach the asymptotic curves of another unstable orbit in a definite way. Finally we study the tangencies and the spirals formed by the asymptotic curves of the orbitsB 1,B 2. We find indications that the number of spiral rotations tends to infinity as ε → ∞. Therefore new tangencies between the asymptotic curves appear for arbitrarily large ε. As a consequence there are infinite new families of stable periodic orbits that appear for arbitrarily large ε.
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  • 16
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    Celestial mechanics and dynamical astronomy 60 (1994), S. 99-129 
    ISSN: 1572-9478
    Keywords: Sitnikov motions ; periodic orbits ; stability ; bifurcations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we deal with the circular Sitnikov problem as a subsystem of the three-dimensional circular restricted three-body problem. It has a first analytical part where by using elliptic functions we give the analytical expressions for the solutions of the circular Sitnikov problem and for the period function of its family of periodic orbits. We also analyze the qualitative and quantitative behavior of the period function. In the second numerical part, we study the linear stability of the family of periodic orbits of the Sitnikov problem, and of the families of periodic orbits of the three-dimensional circular restricted three-body problem which bifurcate from them; and we follow these bifurcated families until they end in families of periodic orbits of the planar circular restricted three-body problem. We compare our results with the previous ones of other authors on this problem. Finally, the characteristic curves of some bifurcated families obtained for the mass parameter close to 1/2 are also described.
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  • 17
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    BIT 34 (1994), S. 62-79 
    ISSN: 1572-9125
    Keywords: AMS(MOS) 65D30 ; 65B05 ; adaptive ; cubature ; singularity ; extrapolation ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A new approach to the integration of vertex singularities is described. This approach is based on a non-uniform subdivision of the region of integration and the technique fits well to the subdivision strategy used in many adaptive algorithms. A nice feature with this approach is that it can be used in any dimension and on any region of integration which can be subdivided into subregions of the same form. The strategy can be applied both to vertex singularities and internal point singularities. In the latter case this can be done without an initial subdivision of the region in order to put the singular point in a vertex. It turns out that the technique has excellent numerical stability properties.
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  • 18
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    Catalysis letters 28 (1994), S. 25-31 
    ISSN: 1572-879X
    Keywords: vanadia/alumina ; stability ; NO x selective reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Changes of the V2O5/Al3O3 catalyst aged for up to 10 years under real conditions of the selective catalytic reduction of NO x by ammonia (SCR) at the tail gases of the nitric acid plant were characterized by51V NMR spectroscopy, porosimetry, temperature programmed reduction (TPR) and catalytic activity measurements. The catalytic activity and the redox properties of the catalyst were found intact. Only small variations of the ratio of the octahedral and tetrahedral vanadia species were documented by51V NMR on aged catalyst.
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  • 19
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    OR spectrum 15 (1994), S. 197-203 
    ISSN: 1436-6304
    Keywords: Inventory ; dynamic programming ; stability ; Lagerhaltung ; Dynamische Optimierung ; Stabilität
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Die Menge der Kostenparameter, für die eine optimale Lösung des dynamischen Losgrößenmodells optimal bleibt wird hier Stabilitätsregion genannt. Die Größe einer solchen Menge kann als Maß der Robustheit einer Lösung angesehen werden. Es ist zu erwarten, daß die Stabilitätsregionen mit wachsendem Zeithorizont schrumpfen und daß sie in diesem Sinne monoton sind. In der vorliegenden Arbeit werden verschiedene hinreichende Bedingungen für diese Monotonie untersucht. Die Bedingungen setzen unter anderem die Existenz von Planungs- und Vorhersage-Horizonten voraus und verallgemeinern so Ergebnisse einer früheren Arbeit, in der Aussagen für gewöhnliche Planungs-Horizonte vorgestellt wurden.
    Notes: Abstract The set of cost inputs for which an optimal solution of the dynamic lot size model remains valid is called stability region. The size of this region may be viewed as a measure of robustness of a solution. It is an expectation that the stability regions shrink with growing time horizons and that they are monotonous in this sense. In the present paper several sufficient conditions implying monotonicity will be studied. The conditions cover the existence of planning and forecast horizons and generalize the results of a previous paper in wich monotonicity results were presented for the case of ordinary planning horizons.
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  • 20
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    Meccanica 29 (1994), S. 195-210 
    ISSN: 1572-9648
    Keywords: Chetaev functional ; pendulum ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Sommario Si considera il problema di stabilità di punti di equilibrio di un pendolo fisico con un filo inestensibile appeso ad esso dal punto di vista del teorema di Lagrange sulla stabilità e sulla sua inversione. Difficoltà specifiche relative allo studio di un sistema meccanico di dimensione infinita sono discusse. Si suggerisce un nuovo metodo per lo studio della stabilità rispetto a due metriche. L'influenza di fenomeni di risonanza sul moto del sistema ridotto (linearizzato) è considerata.
    Notes: Abstract The problem of stability of equilibria of a physical pendulum with a nonstretchable thread attached to it is considered from the standpoint of the Lagrange theorem on stability and its inversion. Specific difficulties which one faces when studying an infinite dimensional mechanical system are discussed. A new approach to the study of stability with respect to two metrics is suggested. The influence of resonant phenomena on the motion of the shortened (linearized) system is considered.
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  • 21
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    Journal of nonlinear science 4 (1994), S. 449-470 
    ISSN: 1432-1467
    Keywords: solitary waves ; stability ; nonlinear dispersive wave equations ; model equations for long waves ; Korteweg-de Vries-type equations ; regularized long-wave equations ; nonlinear Schrödinger equations ; 35B35 ; 35B40 ; 35Q35 ; 35Q51 ; 35Q53 ; 35Q55 ; 35S10 ; 76B15 ; 76B25 ; 76E30 ; 86A05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary After a review of the existing state of affairs, an improvement is made in the stability theory for solitary-wave solutions of evolution equations of Korteweg-de Vries-type modelling the propagation of small-amplitude long waves. It is shown that the bulk of the solution emerging from initial data that is a small perturbation of an exact solitary wave travels at a speed close to that of the unperturbed solitary wave. This not unexpected result lends credibility to the presumption that the solution emanating from a perturbed solitary wave consists mainly of a nearby solitary wave. The result makes use of the existing stability theory together with certain small refinements, coupled with a new expression for the speed of propagation of the disturbance. The idea behind our result is also shown to be effective in the context of one-dimensional regularized long-wave equations and multidimensional nonlinear Schrödinger equations.
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  • 22
    ISSN: 1572-8951
    Keywords: Diazafluorenone ; Schiff-base amphiphiles ; monolayer ; bilayer ; membrane ; stability ; electrochemical oscillations ; chemical sensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new kind of diazafluorenone Schiff base amphiphile has been synthesized from 1,10-phenanthroline. The superior self-assembling properties of the amphiphiles are advantageous for forming surface monolayer and bilayer membranes (BLMs). BLMs formed with these amphiphiles possess very good stability and electrochemical oscillations. The possibility is suggested of developing a new type of chemical sensor with the ability to distinguish various metal ions from the patterns of electrochemical oscillations.
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  • 23
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    Acta applicandae mathematicae 34 (1994), S. 71-81 
    ISSN: 1572-9036
    Keywords: 60F55 ; 60G10 ; 60K15 ; Coupling ; marked-point processes ; regeneration ; stationarity ; stability ; maximal coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Criteria for semi-, wide-sense-, traditional regeneration and a coupling construction of stochastic processes with embedded point processes are presented.
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  • 24
    ISSN: 1573-5028
    Keywords: alcohol dehydrogenase ; cDNA ; enzyme ; tepary ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The zinc-binding long-chain alcohol dehydrogenases from plants and animals exhibit a considerable level of amino acid sequence conservation. While the functional importance of many of the conserved residues is known, the role of others has not yet been determined. We have identified a naturally occurring Adh-1 allele in the legume Phaseolus acutifolius with several unusual characteristics. Individuals homozygous for this allele, Adh-1CN, possess a single isozyme starch gel electrophoretic pattern suggestive of a null allele, and exhibit ADH enzyme activity levels ca. 60% lower than the standard wild-type Adh-1F line. Interestingly, analysis of Adh-1CN homozygotes on an alternative gel system indicates that Adh-1CN does encode a polypeptide capable of forming functional homo- and heterodimers. However, the levels of ADH activity displayed by these isozymes are far lower than those observed for the corresponding wild type ADH-1F isozymes. Dialysis experiments indicate that isozymes containing the ADH-1CN polypeptide are inactivated by slightly acidic conditions, which may explain the apparent null phenotype on starch gels. Elevated temperatures cause a similar loss of enzyme activity. The deduced amino acid sequences of ADH-1CN and ADH-1F were obtained from their corresponding cDNA clones, and the only significant difference detected between the two is a single amino acid replacement substitution. Residue 144 is occupied by phenylalanine in the ADH-1F polypeptide, whereas serine occupies this position in the ADH-1CN polypeptide. The proximity of residue 144 to the catalytic zinc in the substrate-binding pocket, coupled with the fact that it is integral to a defined hydrophobic core of the ADH polypeptide, may explain the observed disruptive effect that the serine substitution has on both the activity and stability of the ADH-1CN polypeptide. It also provides an explanation for the maintenance of phenylalanine or the structurally similar tyrosine at this residue in Zn-binding long-chain ADHs.
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  • 25
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    Journal of mathematical biology 32 (1994), S. 395-426 
    ISSN: 1432-1416
    Keywords: Uniform persistence ; stability ; Lyapunov functional ; level-crossing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Dynamical characteristics of an integrodifferential system modelling two species competition with hereditary effects are investigated; in particular we derive sufficient conditions for the persistence of the species, existence of an attracting periodic solution and ‘level-crossings’ of solutions about the periodic solution.
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  • 26
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    Journal of mathematical biology 32 (1994), S. 515-520 
    ISSN: 1432-1416
    Keywords: Gametophytic incompatibility ; model ; equilibrium ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The deterministic dynamics of the classical single-locus multiple-allele model of gametophytic incompatibility is analyzed with the intention to prove the conjecture that the symmetric state (uniform distribution of genotypes) is the only polymorphic equilibrium and that this equilibrium is globally asymptotically stable in the interior of the frequency simplex. It is shown that the minimum allelic frequency increases strictly over the generations as long as a uniform allelic distribution is not realized. Hence, the minimum allelic frequency is a Ljapunov function for the invariant set of genotypic frequencies characterized by a uniform allelic distribution. Within this set, the uniform genotypic distribution is approached in an exponential fashion, which proves the assertion. An evolutionary optimization rule associated with the global convergence to the symmetric state is implied by the fact that at this state the overall amount of pollen elimination resulting from incompatible crosses is minimized.
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  • 27
    ISSN: 1573-9171
    Keywords: dysprosium(III) ; aminobenzoic acids ; complex ; structure ; stability ; paramagnetic birefringence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Steric structures of dysprosium(III) aminobenzoate complexes with the 1∶1 and 1∶2 molar ratio in aqueous solutions were determined on the basis of pH-metric and paramagnetic birefringence data. An increase in conjugation observed for the series of the acids,viz., benzoic,meta-, ortho-, andpara-aminobenzoic acids, results in the increased stability of the complexes with the 1∶1 and 1∶2 composition. In the case ofpara-aminobenzoic acid, the polyhedra [DyL(H2O)6]2+ and [DyL2(H2O)4]+ are cubes with the ligands coordinated to one and two edges, respectively. In the case ofmeta-aminobenzoic acid, the polyhedra [DyL(H2O)6]2+ and [DyL2(H2O)4]+ are a dodecahedron with the ligand coordinated to one edge and a square anti-prism with the ligands coordinated to two edges, respectively. In the case ofortho-aminobenzoic acid, both the 1∶1 and 1∶2 complexes have structures that are intermediate between the structures ofmeta- andpara-aminobenzoic acids.
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    Acta mechanica Sinica 10 (1994), S. 311-325 
    ISSN: 1614-3116
    Keywords: finite deformation ; rigid-perfect plasticity ; stability ; extremum principles ; plastic limit analysis ; post-yield analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The post yield behavior of rigid-perfectly plastic solids at the collapse load is studied based on the finite deformation theory. By using the general duality theory developed by Gao-Strang (1989), a global stability criteria is proposed and a pair of dual extremum principles, expressed in terms of displacements, displacement rates and the Kirchhoff stresses are established for plastic collapse analysis. It is proved that under large deformations, the existence of the plastic limit state at the collapse load depends on the directional derivative of a so-called complementary gap function. The application to the nonlinear plastic collapse theory yields a pair of dual bounding theorems for limit loading factor associated with any transient displacement of the deformed body when the global extremum criteria are satisfied.
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    Numerical algorithms 8 (1994), S. 201-220 
    ISSN: 1572-9265
    Keywords: Automatic ; adaptive ; cubature ; singularity ; extrapolation ; stability ; 65D30 ; 65-04 ; 65B05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We describe an automatic cubature algorithm for functions that have a singularity on the surface of the integration region. The algorithm combines an adaptive subdivision strategy with extrapolation. The extrapolation uses a non-uniform subdivision that can be directly incorporated into the subdivision strategy used for the adaptive algorithm. The algorithm is designed to integrate a vector function over ann-dimensional rectangular region and a FORTRAN implementation is included.
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  • 30
    ISSN: 1573-0646
    Keywords: carzelesin (U-80,244) ; analytical characterization ; parenteral formulation ; stability ; degradation products
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The aim of this study was to design a parenteral dosage form for the investigational cytotoxic drag carzelesin. A stable formulation in PET (Polyethylene glycol 400/absolute ethanol/Tween 80, 6:3:1, v/v/v) was developed. The prototype, containing 0.50 mg carzelesin in 2.0 ml PET formulation, was found to be the optimal formulation in terms of solubility, stability and dosage requirements in phase I clinical trials. Quality control of the formulation showed that the pharmaceutical preparation of carzelesin in PET is not negatively influenced by the manufacturing process. Shelf life studies demonstrated that the formulation is stable for at least 1 year, when stored at −30°C in the dark. In addition, the stability of carzelesin in the PET formulation is discussed as a function of temperature, additives and after dilution in infusion fluids.
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  • 31
    ISSN: 1573-904X
    Keywords: peptides ; liquid crystals ; stability
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    Topics: Chemistry and Pharmacology
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  • 32
    ISSN: 1573-904X
    Keywords: chimeric antibody ; protein ; stability ; multiple freezing and thawing ; aggregation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Chimeric L6 is a mouse–human monoclonal antibody specific for tumor cell-associated antigens. The factors affecting the physical and chemical stability of chimeric L6 were assessed at elevated temperatures (30–60°C) and by multiple freezing and thawing. Three routes of degradation were observed: chemical degradation to smaller molecular weight species, irreversible aggregation, and formation of a reversible dimer. The specific pathway depended on the stress condition applied and the pH, with maximal overall stability to both thermal stress and multiple freezing/thawing observed at about pH 5.5. Other factors including antibody concentration, buffer concentration, NaCl concentration, and agitation had minimal influence on the stability. Commonly used sugars, polyhydric alcohols, and amino acids effectively prevented freeze/thaw-induced aggregation.
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  • 33
    ISSN: 1573-904X
    Keywords: cyclodextrin ; equilibrium model ; nasal delivery ; peptides ; peptidase ; stability
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Leucine enkephalin (YGGFL) undergoes rapid degradation in sheep nasal mucosa to yield GGFL which is further degraded to FL. The activity of the nasal mucosal homogenate against YGGFL and GGFL (t1/212 and 7 min) was significantly greater than that observed with a nasal wash fluid (t1/2 40 and 13 min). The effect of cyclodextrins on the rate of degradation of FGG and YGGFL by leucine aminopeptidase (LAP) and of GGF by carboxypeptidase A (CPA) was monitored. Little effect was observed with FGG (with LAP) but the half-life of YGGFL (with LAP) was extended from ~44 min to ~75 min in the presence of a 25-fold excess of β-cyclodextrin. The stability of GGF (with CPA) was also enhanced; an effect was observable with a 5-fold excess of cyclodextrin and the half-life could be extended by 40–75%. An equation is presented which allows the estimation of the concentration of free peptide in the peptide-cyclodextrin solutions.
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  • 34
    ISSN: 1573-904X
    Keywords: taxol ; mixed micelles ; liposomes ; formulation ; solubility ; stability ; antitumor activity ; acute toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Taxol is a promising antitumor agent with poor water solubility. Intravenous administration of a current taxol formulation in a non-aqueous vehicle containing Cremophor EL may cause allergic reactions and precipitation upon aqueous dilution. In this study a novel approach to formulate taxol in aqueous medium for i.v. delivery is described. The drug is solubilized in bile salt (BS)/phospholipid (PC) mixed micelles. The solubilization potential of the mixed micelles increased as the total lipid concentration and the molar ratio of PC/BS increased. Precipitation of the drug upon dilution was avoided by the spontaneous formation of drug-loaded liposomes from mixed micelles. The formulation can be stored in a freeze-dried form as mixed micelles to achieve optimum stability, and liposomes can be prepared by simple dilution just before administration. As judged by a panel of cultured cell lines, the cytotoxic activity of taxol was retained when formulated as a mixed-micellar solution. Further, for the same solubilization potential, the mixed-micellar vehicle appeared to be less toxic than the standard nonaqueous vehicle of taxol containing Cremorphor EL.
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    Evolutionary ecology 8 (1994), S. 150-171 
    ISSN: 1573-8477
    Keywords: bottom-up effects ; food chain ; functional response ; limit cycle ; predator ; prey ; stability ; topdown effects ; trophic structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This article investigates the mean abundances of trophic levels in simple models of two- and three-level food chains as a function of the rate of input of nutrients. The analysis concentrates on cases in which the equilibrium point with all species present is unstable. In most of the models, the instability arises because the consumer species become satiated when food density is high. In unstable two-level systems, bottom level abundance generally increases with increased nutrient input. The abundance of the second level may decrease with increased input. Changes in the intrinsic rate of increase and carrying capacity of the bottom level can have qualitatively opposite effects on trophic level abundances. Refuges for or immigration of the bottom level usually cause both levels to increase in mean abundance with an increased carrying capacity. A variety of different predator—prey models are discussed briefly and the results suggest that increased nutrient input will often increase the abundance of both levels; however, several circumstances can cause the top level to decrease. In three-level systems, an increased carrying capacity can cause extinction of the top level. Extinction may or may not be conditional on the initial densities of the three levels. These results may help explain the observed lack of correlation between productivity and the number of trophic levels in natural food webs, as well as the lack of very long food chains. The results suggest that patterns of abundances across productivity gradients cannot be used to assess the importance of top-down vs bottom-up effects.
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    Colloid & polymer science 272 (1994), S. 1166-1173 
    ISSN: 1435-1536
    Keywords: Gel-emulsions ; ESR spin-probe method ; order parameter ; isotropic hyperfine splitting constant ; correlation time ; stability
    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 W/O gel-emulsions (high-internal-phase-volume-ratio emulsions) form in water (or brine) /tetraethyleneglycol dodecyl ether/heptane system above the HLB (hydrophile-lipophile balance) temperature of the system. A salt, which largely decreases cloud temperature in a water-nonionic surfactant system, makes the surfactant film rigid and the gel-emulsions hence become very stable. The effect of aded salt on the apparent order parameter “S”, and the isotropic hyperfine splitting constant “a N” in gel-emulsions was determined by the ESR spin probe method using 5-doxyl stearic acid as the spin probe. The apparent order parameter “S”, and the isotropic hyperfine splitting constant “a N” increase with increasing salinity in Na2SO4, CaCl2, and NaCl systems. It is considered that the surfactant molecules are tightly packed in these systems and this tendency is highly related to the stability of gel-emulsions. The salt dehydrates the hydrophilic moiety of surfactant and hence the lateral interactions of surfactant molecular layer at the water-oil interface increases. The observed difference in the apparent order parameter between the ordinary emulsions and the gel-emulsions suggests that most of the surfactant molecules are adsorbed at the oil-water interface (the surface of the water droplet) in gel-emulsions.
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  • 37
    ISSN: 1435-1536
    Keywords: Microgel ; poly(N-isopropyl-acrylamide) ; surface methylation ; stability ; aggregation
    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 stability of thermoreversible microgel particles of poly(N-isopropylacrylamide) having carboxylate surface charge groups has been studied in the presence of electrolyte and non-adsorbing polymer. Methylation of the surface charge groups leads to a decrease in the electrophoretic mobility of the particles and also the interparticle electrostatic repulsive potential, resulting in the material becoming more susceptible to flocculation. The Hamaker constant of the microgel particles increases with the decrease in the hydrodynamic size of the particles following heating. This brings about an increase in the van der Waals attractive energy which results in the particles aggregating in the presence of sufficient electrolyte. Under conditions of flow through membranes, where shearing forces are operative, the flocculation observed following the heating of the dispersions results in the blockage of pores.
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    Geotechnical and geological engineering 12 (1994), S. 113-121 
    ISSN: 1573-1529
    Keywords: Greywacke ; normal stress ; rockfill ; shear strength ; stability ; triaxial testing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary Accurate stability analysis must consider the variation of the angle of friction of rockfill with the confining pressure. In reality, with increasing depth of a rockfill dam, the apparent friction angle decreases, whereas near the surface it tends to be higher. Conventional methods which employ a constant friction angle throughout the depth of a rockfill shell often yield a lower factor of safety (conservative) for shallow slip planes. On the contrary, they produce a higher factor of safety for deepseated slips subjected to increased normal (confining) stresses. This paper compares the constant friction angle approach with the variable friction angle method based on the stability analysis of a large rockfill dam, and the associated practical implications are discussed. In the latter analysis, the effect of normal stress on the friction angle of rockfill is incorporated through experimental observations.
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    Multidimensional systems and signal processing 5 (1994), S. 307-318 
    ISSN: 1573-0824
    Keywords: Eigenvalue ; matrix ; polytope ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A simple geometric test can be applied to evaluateG-stability of a polytope of matrices. In case of a regionG being a convex subset of the complex plane, it suffices to assume that four (for some regions even less) corner points of a certain rectangle are contained inG.
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  • 40
    ISSN: 1573-5060
    Keywords: PCR ; polymorphisms ; DNA ; RAPDs ; rye ; Secale cereale ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Cultivar specific DNA profiles in rye were revealed by polymerase chain reaction (PCR) using randomly amplified polymorphic DNA (RAPD) sequences. Ten base primers were used for the amplification of genomic DNA of rye cultivars by PCR. RAPD analysis was found to be reproducible among samples between PCR runs. When amplification profiles of different rye cultivars were compared using various primers, the overall profiles were cultivar specific. However, not all primers revealed polymorphisms. These primers appear to amplify conserved sequences in all rye cultivars. Intracultivar studies were conducted on two of the cultivars. In the cultivar Imperial, no polymorphisms were observed among ten plants analyzed with five primers. In the cultivar Balboa, polymorphisms were observed among fifty plants with four of the ten primers analyzed. Despite the small amount of intracultivar variability, RAPD analysis has the potential to be a rapid and reliable method of cultivar identification in this outcrossing species.
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    Euphytica 77 (1994), S. 221-230 
    ISSN: 1573-5060
    Keywords: Variety trials ; progeny testing ; timothy ; stability ; G × E interactions ; adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A joint breeding project for the northern areas of Scandinavia and Iceland was initiated in 1981 under the auspices of the Nordic Council of Ministers. Initially, efforts concentrated on cooperative trials in which both early and more advanced breeding material was tested at a number of experimental stations in the northern regions. This was followed by a joint breeding programme for timothy with the primary aim of developing varieties that possess broad adaptation to a range of Nordic climates and managements and can be grown throughout the northernmost part of Scandinavia. Each of the five national breeding stations originally provided 12 timothy genotypes for the project giving a total of 60 genotypes. The parental genotypes were compared as spaced plants at all five stations and their polycross progeny were grown under sward conditions at the same sites. On the basis of results obtained from these field trials parent clones have been selected and intercrossed to form synthetic populations.
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    Journal of optimization theory and applications 81 (1994), S. 277-296 
    ISSN: 1573-2878
    Keywords: Robust control ; min-max techniques ; synthesis methods ; stability ; multivariable control systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An important (some say, the major) reason for using feedback control is the presence of uncertain parameters which are a natural part of any real dynamical model. In this paper, we consider uncertain constant parameters in a time-invariant linear plant and announce some new results concerning robust compensator synthesis. Using the min-max principle, we derive necessary conditions for fixed-order linear robust controllers assuring asymptotic stability or relative stability. These necessary conditions are an extension of the Lagrange multiplier method. This is achieved using a cost function based on the inverse of the so-called critical constraint. We present both matrix and polynomial versions; the latter allows controllers of fixed structure. We suggest a probability-one homotopy algorithm and solve some examples from the literature.
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    Applied mathematics and mechanics 15 (1994), S. 1035-1045 
    ISSN: 1573-2754
    Keywords: mutual interference system ; bounded ; extermination equilibrium ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper considers a typical mutual interference system of four-dimensional species, its bounded, extermination stability are studied, and their necessary-sufficient condition are given, and their ecology meaning set forth.
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    Applied mathematics and mechanics 15 (1994), S. 923-928 
    ISSN: 1573-2754
    Keywords: stability ; multi-scale perturbation method ; bifurcation from infinity
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper applies the multi-scale perturbation method suggested by Ref. [3] to investigate the linear stability behavior of distorted plane Couette flow. Using this method, the unstable Tollmien-Schlichting wave in plane Couette flow can be found. but not the most unstable mode. By comparing the results of this paper with those of Ref. [3], the effectiveness of this method is investigated.
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    Periodica mathematica Hungarica 29 (1994), S. 81-87 
    ISSN: 1588-2829
    Keywords: Primary 39 ; Secondary 58F ; Generalized logistic ; stability ; difference equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
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  • 46
    ISSN: 1573-904X
    Keywords: biodegradation ; stability ; α-chymotrypsin ; cyclodextrins ; enteral absorption ; histology ; insulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The relative effectiveness of two β-cyclodextrin derivatives, i.e., dimethyl-β-cyclodextrin (DMβCD) and hydroxypropyl-β-cyclodextrin (HPβCD), in enhancing enteral absorption of insulin was evaluated in the lower jejunal/upper ileal segments of the rat by means of an in situ closed loop method. The incorporation of 10% (w/v) DMβCD to a 0.5 mg/ml porcine-zinc insulin solution dramatically increased insulin bioavailability from a negligible value (~0.06%) to 5.63%, when administered enterally at a dose of 20 U/kg. However, addition of 10% (w/v) HPβCD did not improve enteral insulin uptake significantly with a bioavailability of only 0.07%. Similarly, the pharmacodynamic relative efficacy values obtained after the enteral administration of 20 U/kg insulin, 20 U/kg insulin with 10% HPβCD, and 20 U/kg insulin with 10% DMβCD were 0.24%, 0.26%, and 1.75%, respectively. Biodegradation studies of 0.5 mg/ml insulin hexamers by 0.5 µM α-chymotrypsin revealed no inhibitory effect on the enzymatic activity by the two cyclodextrins. On the contrary, the apparent first-order rate constant increased significantly in the presence of 10% DMβCD, suggesting insulin oligomer dissociation by DMβCD. Histopathological examination of the rat intestine was performed to detect tissue damage following enteral administration of the β-cyclodextrin derivatives. Light microscopic inspection indicated no observable tissue damage, thereby arguing direct membrane fluidization as the primary mechanism for enhanced insulin uptake. This study indicates the feasibility of using cyclodextrins as mucosal absorption promoters of proteins and peptide drugs.
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  • 47
    ISSN: 1573-904X
    Keywords: oligodeoxynucleotides ; antisense ; chloramphenicol acetyltransferase ; nucleases ; phosphorothioate ; stability ; T m ; human plasma
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    Topics: Chemistry and Pharmacology
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    Journal of optimization theory and applications 83 (1994), S. 565-586 
    ISSN: 1573-2878
    Keywords: Variational inequalities ; range sets ; cones ; polyhedra ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper investigates the closedness and convexity of the range sets of the variational inequality (VI) problem defined by an affine mappingM and a nonempty closed convex setK. It is proved that the range set is closed ifK is the union of a polyhedron and a compact convex set. Counterexamples are given such that the range set is not closed even ifK is a simple geometrical figure such as a circular cone or a circular cylinder in a three-dimensional space. Several sufficient conditions for closedness and convexity of the range set are presented. Characterization for the convex hull of the range set is established in the case whereK is a cone, while characterization for the closure of the convex hull of the range set is established in general. Finally, some applications to stability of VI problems are derived.
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    Environmental and resource economics 4 (1994), S. 241-249 
    ISSN: 1573-1502
    Keywords: Economic growth ; pollution control ; technical progress ; tradeable pollution permits ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Economics
    Notes: Abstract The papers on economic growth with environmental constraints usually ignore the effect of technical progress, this results in static steady state solutions. This paper examines the problem of optimal economic growth with environmental damage, technical progress taken into account, which produces a steady state solution that corresponds to an equilibrium growth, with non-constant emissions and pollutant stock. As a means of steering the economy along the optimal path, two types of tradeable pollution permits are analyzed. The method of stabilizing the optimal path, leading to a steady state, is suggested.
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    Nonlinear dynamics 5 (1994), S. 39-52 
    ISSN: 1573-269X
    Keywords: Shaft ; stability ; bifurcation ; analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The dynamic stability and self-excited posteritical whirling of rotating transversally loaded shaft made of a standard material with elastic and viscous nonlinearities are analyzed in this paper using the theory of bifurcations as a mathematical tool. Partial differential equations of motion are derived under assumption that von Karman's nonlinearity is absent but geometric curvature nonlinearity is included. Galerkin's first-mode discretization procedure is then applied and the equations of motion are transformed to two third-order nonlinear equations that are analyzed using the theory of bifurcation. Condition for nontrivial equilibrium stability is determined and a bifurcating periodic solution of the second-order approximation is derived. The effects of dimensionless stress relaxation time and cubic elastic and viscous nonlinearities as well as the role of the transverse load are studied in the exemplary numerical calculations. A strongly stabilizing influence of the relaxation time is found that may eliminate self-excited vibration at all. Transition from super- to subcritical bifurcation is observed as a result of interaction between system nonlinearities and the transverse load.
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