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  • 1990-1994  (10,461)
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  • Articles  (10,461)
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  • 1
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    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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  • 28
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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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 35
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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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    Journal of Chemometrics 8 (1994), S. 21-36 
    ISSN: 0886-9383
    Keywords: GRAM ; Tucker ; Unfold ; NBRA ; Second-order ; Three-way ; PARAFAC ; Trilinear ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If an analytical instrument or instrumental method gives a response matrix when analyzing a pure analyte, the instrument or instrumental method is called a second-order method. Second-order methods that generate a response matrix for a pure analyte of rank one are called rank-one second-order methods. If the response matrix of a pure analyte is not rank one, essentially two cases exist: medium rank (between two and five) and high rank (greater than five). Subsequently, medium- and high-rank second-order calibration tries to use medium- and high-rank second-order methods to analyze for analytes of interest in a mixture. A particular advantage of second-order methods is the ability to analyze for analytes of interest in a mixture which contains unknown interferences. Keeping this advantage is the challenge on moving away from rank-one second-order calibration methods. In this paper a medium-rank second-order calibration method is proposed based on least-squares restricted Tucker models. With this method the second-order advantage is retained.
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    Journal of Chemometrics 8 (1994), S. 101-101 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 45
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    Journal of Chemometrics 8 (1994), S. 103-110 
    ISSN: 0886-9383
    Keywords: Taguchi ; Robust design ; Design of experiments ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper is intended to convey the essence of Taguchi's design approach to chemists and others with an interest in chemometrics. Although most Taguchi-style applications worldwide have been in electronics and in elaborately transformed manufactures, examples are increasingly found in chemical processes and in the food industry.Foremost among Taguchi's contributions is the concept of designing processes and products to be robust to the uncontrollable environmental influences which they experience during their operation or lifetime. This concept is explained with a worked example.
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    Journal of Chemometrics 8 (1994), S. 127-145 
    ISSN: 0886-9383
    Keywords: Compression ; Multivariate analysis ; B-splines ; FT-IR spectra ; Second-order ; Two-dimensional ; Hyphenated methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to improve the storage and CPU time in the numerical analysis of large two-dimensional (hyphenated, second-order) infrared spectra, a data-preprocessing technique (compression) is presented which is based on B-splines. B-splines have been chosen as the compression method since they are wellsuited to model smooth curves. There are two primary goals of compression: a reduction of file size and a reduction of computation when analyzing the compressed representation. The compressed representation of the spectra is used as a substitute for the original representation. For the particular example used here, approximately 0.16 bit per data element was required for the compressed representation in contrast with 16 bits per data element in the uncompressed representation. The compressed representation was further analysed using principal component analysis and compared with a similar analysis on the original data set. The results shows that the principal compotent model of the compressed representation is directly comparable with the principal component model of the original data.
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  • 47
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. i 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 181-203 
    ISSN: 0886-9383
    Keywords: RAFA ; GRAM ; Eigenvalues ; Bias ; Variance ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rank annihilation factor analysis (RAFA) is a method for multicomponent calibration using two data matrices simultaneously, one for the unknown and one for the calibration sample. In its most general form, the generalized rank annihilation method (GRAM), an eigenvalue problem has to be solved. In this second paper expressions are derived for predicting the bias and variance in the eigenvalues of GRAM. These expressions are built on the analogies between a reformulation of the eigenvalue problem and the prediction equations of univariate and multivariate calibration. The error analysis will also be performed for Lorber's formulation of RAFA. It will be demonstrated that, depending on the size of the eigenvalue, large differences in performance must be expected. A bias correction technique is proposed that effectively eliminates the bias if the error in the bias estimate is not too large. The derived expressions are evaluated by Monte Carlo simulations. It is shown that the predictions are satisfactory up to the limit of detection. The results are not sensitive to an incorrect choice of the dimension of the factor space.
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    Journal of Chemometrics 8 (1994), S. 243-243 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 51
    ISSN: 0886-9383
    Keywords: Fitting ; Non-linear ; Least squares ; Refinement ; Constraints ; MSE ; Confidence ; C ls ; XPS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A non-linear least squares iterative refinement has been implemented which shows high performance on a multiple-peak spectrum including baseline or background. Constraints as well as links within a range are introduced to drive the mathematical optimization: each peak parameter (i.e. height, position, Gaussian/Lorentzian mixing ratio and HWHM on both left and right sides) has assigned to it an allowed range of variation and can be strained to be correlated with other parameters belonging either to the same peak (symmetrical peaks) or to other peaks (doublets, triplets, etc.). Peak shapes typical of XP spectra are used and applications in the field of XPS are discussed. Through emulated curves with Poisson distributed noise, the accuracy and precision of back-calculated (refined) parameters have been estimated. Moreover, a confidence level calculated from X2 and degrees of freedom has been suggested to check the overall fitting of experimental curves where the signal-to-noise ratio is a priori unknown. An application to real C ls XP spectra is described as an example and a list of suggestions is given to match operator requirements. Finally, features of NLLSRC are discussed with respect to other approaches.
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    Journal of Chemometrics 8 (1994), S. 263-272 
    ISSN: 0886-9383
    Keywords: Molecular descriptors ; Principal component analysis ; Chemometrics ; Pattern recognition ; Total surface area ; PCDD PCDF ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New theoretical molecular indices are defined. They contain information about the whole molecular structure in terms of size, shape, symmetry and atom distribution. These indices are calcualted from the (x, y, z) co-ordinates of a molecule within different weighting schemes in a straightforward manner and represent a very general approach to describe molecules, molecular fragments, macromolecules and molecular conformations in a unitary conceptual framework. Their interpretability is quite evident and is defined by the same mathematical properties as the algorithm used for their calculation. Examples on the total surface area, toxicity of PCDD and PCDF and reaction rate of catalysed reactions show a high modelling power of these indices.
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    Journal of Chemometrics 8 (1994), S. 301-302 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 8 (1994), S. 333-347 
    ISSN: 0886-9383
    Keywords: PLS ; ATR ; Paper ; Resolution ; Infrared ; FTIR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Attenuated total reflectance Fourier transform infrared spectrometry (ATR-FTIR) has been used to determine the amount of styrene-butadiene latex on the surface of coated papers and to predict the composition of the polymer. Spectrum recording was performed on the sample in its usual form without any modification.For quantitative analysis, partial least squares (PLS) regression, principal component regression (PCR) and multi-linear regression (MLR) were used to calculate models for prediction. The best result is obtained with PLS.We analysed two series of paper samples. The first analysis concerns the measurement of the quantity of latex of a constant quality on the coating surface. For 15 samples the concentration varied between 5 and 25 parts (grams per 100g of mineral pigments). We compared the predictive results at various resolutions. We obtained a relative error of 0.15 parts in latex at 4 cm-1 resolution. The second analysis concerns the measurement of the styrene/butadiene ratio in various types of latex. We obtained a relative error of 0.156 parts for styrene determination and 0.161 parts for butadiene determination.
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    Journal of Chemometrics 8 (1994), S. 375-376 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 391-407 
    ISSN: 0886-9383
    Keywords: Neural networks ; Non-linear multivariate regression ; Pattern classification ; Kalman filter ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Finding methods for the optimization of weights in feedforward neural networks has become an ongoing developmental process in connectionist research. The current focus on finding new methods for the optimization of weights is mostly the result of the slow and unreliable convergence properties of the gradient descent optimization used in the original back-propagation algorithm. More accurate and computationally expensive second-order gradient methods have displaced earlier first-order gradient optimization of the network connection weights. The global, extended Kalman filter is among the most accurate and computationally expensive of these second-order weight optimization methods. The iterative, second-order nature of the filter results in a large number of calculations for each sweep of the training set. This can increase the training time dramatically when training is conducted with data sets that contain large numbers of training patterns. In this paper an adaptive variant of the global, extended Kalman filter that exhibits substantially improved convergence properties is presented and discussed. The adaptive mechanism permits more rapid convergence of network training by identifying data that contain redundant information and avoiding calculations based on this redundant information.
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    Journal of Chemometrics 8 (1994), S. 439-443 
    ISSN: 0886-9383
    Keywords: Pattern recognition ; Principal component analysis ; Inverse mapping ; Optimization ; Material design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An inverse mapping method called PCB (principal component backing), in which the point representing an unknown sample from a low-dimensional principal component subspace is back-projected to the high-dimensional original feature space, is proposed. Two sorts of boundary conditions, non-linear inverse mapping and linear inverse mapping, are used to obtain an accurate solution in the PCB method. The method is applied to the material design of high-Tc superconductors, predicting the composition and process conditions for the synthesis of F-doped Bi-based materials. Samples in the ‘optimal’ region with the highest Tc of the Bi-based ceramics have been predicted.
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    Journal of Chemometrics 8 (1994) 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 37-44 
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    Keywords: Bootstrap ; Confidence interval ; Non-linear regression ; Monte Carlo methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Non-linear regression models describing the toxicity of a mixture of rotenone and pyrethrins as an insecticide, the catalytic dehydration of n-hexyl alcohol and the Michaelis-Menten model for characterizing reaction rates in enzyme systems will be used to illustrate the accuracy of bootstrap methods in non-linear regression. Classical and bootstrap confidence intervals for the parameter estimates will be presented.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 102-102 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 111-125 
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    Keywords: PLS regression algorithm ; Kernel ; Many-variable data sets ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast PLS regression algorithm dealing with large data matrices with many variables (K) and fewer objects (N) is presented For such data matrices the classical algorithm is computer-intensive and memory-demanding. Recently, Lindgren et al. (J. Chemometrics, 7, 45-49 (1993)) developed a quick and efficient kernel algorithm for the case with many objects and few variables. The present paper is focused on the opposite case, i.e. many variables and fewer objects. A kernel algorithm is presented based on eigenvectors to the ‘kernel’ matrix XX TYYT, which is a square, non-symmetric matrix of size N × N, where N is the number of objects. Using the kernel matrix and the association matrices XXT (N × N) and YYT (N × N), it is possible to calculate all score and loading vectors and hence conduct a complete PLS regression including diagnostics such as R2. This is done without returning to the original data matrices X and Y. The algorithm is presented in equation form, with proofs of some new properties and as MATLAB code.
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    Journal of Chemometrics 8 (1994), S. 169-174 
    ISSN: 0886-9383
    Keywords: Kernel algorithm ; PLS ; SVD ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lindgren et al. (J. Chemometrics, 7, 45-49 (1993)) published a so-called kernel algorithm for PLS regression of Y against X when the number of objects is very large. The algorithm is based solely on deflation of the cross-product matrices XTX, YTY and XTY. The algorithm is now described in a shorter and more transparent way and compared with a similar algorithm for the singular value decomposition of XTY.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 241-241 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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  • 66
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    Journal of Chemometrics 8 (1994), S. 273-285 
    ISSN: 0886-9383
    Keywords: GRAM ; Least-squares problem ; Eigenvalue problem ; NIPALS ; Performance index ; Condition number ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we discuss the practical implementation of the generalized rank annihilation method (GRAM). The practical implementation comes down to developing a computer program where two critical steps can be distinguished: the construction of the factor space and the oblique rotation of the factors. The construction of the factor space is a least-squares (LS) problem solved by singular value decomposition (SVD), whereas the rotation of the factors is brought about by solving an eigenvalue problem. In the past several formulations for GRAM have been published. The differences essentially come down to solving either a standard eigenvalue problem or a generalized eigenvalue problem. The first objective of this paper is to discuss the numerical stability of the algorithms resulting from these formulations. It is found that the generalized eigenvalue problem is only to be preferred if the construction of the factor space is not performed with maximum precision. This is demonstrated for the case where the dominant factors are calculated by the non-linear iterative partial least-squares (NIPALS) algorithm. Several performance measures are proposed to investigate the numerical accuracy of the computed solution. The previously derived bias and variance are proposed to estimate the number of physically significant digits in the computed solution. The second objective of this paper is to discuss the relevance of theoretical considerations for application of GRAM in the presence of model errors.
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    Journal of Chemometrics 8 (1994), S. 299-301 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
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    Journal of Chemometrics 8 (1994), S. i 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 349-363 
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    Keywords: Variable selection ; PLS ; Calibration ; Modelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modified PLS algorithm is introduced with the goal of achieving improved prediction ability. The method, denoted IVS-PLS, is based on dimension-wise selective reweighting of single elements in the PLS weight vector w. Cross-validation, a criterion for the estimation of predictive quality, is used for guiding the selection procedure in the modelling stage. A threshold that controls the size of the selected values in w is put inside a cross-validation loop. This loop is repeated for each dimension and the results are interpreted graphically. The manipulation of w leads to rotation of the classical PLS solution. The results of IVS-PLS are different from simply selecting X-variables prior to modelling. The theory is explained and the algorithm is demonstrated for a simulated data set with 200 variables and 40 objects, representing a typical spectral calibration situation with four analytes. Improvements of up to 70% in external PRESS over the classical PLS algorithm are shown to be possible.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 409-421 
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    Keywords: Deconvolution ; FT-IR spectroscopy ; Protein conformations ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: In a variety of spectroscopic techniques the fundamental problem exists of determination of the individual spectral components, intrinsically overlapped in the measured spectrum. This is a typical deconvolution problem and several methods and techniques have been proposed for its solution in the technical literature, but suggestions of new approaches are still of interest. A new deconvolution procedure is presented here based on the use of the conjugate gradient minimization algorithm with the addition of sutiable constraints directly obtained by the application to the measured spectrum of the second-derivative operator or more sophisticated resolution enhancement procedures. Since in the examined case deconvolution essentially requires the minimization of a non-convex function, the use of such constraints is extremely important to supply suitable input parameters to the conjugate gradient algorithm to avoid obtaining minimum points which have no physical meaning. In our case each spectral compoent used for deconvolution has been assumed to have a Gaussian analytical definition fully identified by three parameters (amplitude, central frequency, spectral bandwidth), so that the input values required to start the deconvolution process are the number M of Gaussian components and 3M suitable initial approximations of the parameters above. It is shown that all this information can be obtained from the measured data. The deconvolution procedure was implemented by a FORTRAN Microsoft Version 5.1 program and experimental results relative to spectroscopic data obtained by FT-IR analysis of human serum albumin are reported. The results are discussed and compared with data obtained by the use of other techniques.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. i 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 1-20 
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    Keywords: Discriminant analysis ; Least squares ; Prediction ; Regression ; Relationship ; Structure ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Twenty-two contrasting statistical methods are reviewed for their applicability to QSAR studies and similar prediction-oriented fields. Each method is concisely specified prior to explanatory or critical comment.
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    Journal of Chemometrics 8 (1994), S. 65-79 
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    Keywords: Genetic algorithms ; Full validation ; Feature selection ; Outlier detection ; Multivariate analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Genetic algorithms have been proved to be a very efficient method in the feature selection problem. However, as for every other method, if the validation of the results is performed in an incomplete way, erroneous conclusions can be drawn. In this paper a development of a previous genetic algorithm is presented so that a full validation of the results can be obtained. Furthermore, this algorithm has been shown to perform very well also as an outlier detector, allowing easy identification of the presence of outliers even in cases where the ‘classical’ techniques fail.
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    Journal of Chemometrics 8 (1994), S. 81-93 
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    Keywords: Sensory evaluation ; Cumulative ranks ; Assessor variation ; Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: A graphical method of assessing differences between sets of rankings based on cumulative ranks is developed. The method can be used to identify rankings that differ over all or just part of the range of objects ranked. The method is applied to an example of sensory evaluation of green peas in which ten assessors scored six attributes on each of 60 samples.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 305-331 
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    Keywords: Pyrolysis ; Mass spectroscopy ; Multivariate analysis ; Biological material identification ; Convexity ; Cones ; Subspaces ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This work addresses the classification of high-dimensional time-dependent pyrolysis mass spectra of biological samples. The aim was the detection and classification of biological agents, and the developed approach resembles mixture analysis. The data were projected on to a low-dimensional subspace using singular value decomposition. Then a convex cone was formed on this subspace, showing as its corners physically meaningful components of the sample. This technique enabled separation of a biological material signal largely independent of the absolute amount of sample. The detection of the presence of any biological material could be accomplished based on the convex cone alone, without other reference to the mass spectra. Automated clustering of samples was successfully carried out using a minimal spanning tree.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 377-389 
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    Keywords: Kernel PLS regression ; Cross-validation ; Model dimensionality ; Multivariate image regression ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multivariate images are very large data structures and any type of regression for their analysis is very computer-intensive. Kernel-based partial least squares (PLS) regression, presented in an earlier paper, makes the calculation phase more rapid and less demanding in computer memory. The present paper is a direct continuation of the first paper. In this study the kernel PLS algorithm is extended to include cross-validation for determination of the optimal model dimensionality. To show the applicability of the kernel algorithm, two examples from multivariate image analysis are used. The first example is an image from an airborne scanner of size 9 × 512 × 512. It consists of nine images which are regressed against a constructed dependent image to test the accuracy of the kernel algorithm when used on large data structures. The second example is a satellite image of size 7 × 512 × 512. Several different regression models are presented together with a comparison of their predictive capabilities. The regression models are also used as examples for showing the use of cross-validation.
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    Journal of Chemometrics 8 (1994), S. 99-100 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 147-154 
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    Keywords: RAFA ; GRAM ; Eigenvalue problem ; Complex solution ; Degenerate solution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rank annihilation factor analysis (RAFA) is a method for multicomponent calibration using two data matrices simultaneously, one for the unknown and one for the calibration sample. In its most general form, the generalized rank annihilation method (GRAM), an eigenvalue problem has to be solved. In this first paper different formulations of GRAM are compared and a slightly different eigenvalue problem will be derived. The eigenvectors of this specific eigenvalue problem constitute the transformation matrix that rotates the abstract factors from principal component analysis (PCA) into their physical counterparts. This reformulation of GRAM facilitates a comparison with other PCA-based methods for curve resolution and calibration. Furthermore, we will discuss two characteristics common to all formulations of GRAM, i.e. the distinct possibility of a complex and degenerate solution. It will be shown that a complex solution-contrary to degeneracy-should not arise for components present in both samples for model data.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 179-180 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 287-292 
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    Keywords: Rank annihilation ; Principal components ; Procrustes rotation ; Multivariate analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that the DATa ANalysis (DATAN) algorithm can be expressed in terms of rank annihilation factor analysis (RAFA). Subsequent advances in RAFA are applied to DATAN to eliminate the problems and restrictions associated with DATAN. The extension of DATAN in terms of the trilinear decomposition algorithm is discussed.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 365-370 
    ISSN: 0886-9383
    Keywords: Censored data ; ECM and EM algorithms ; Incomplete data ; Maximum likehhood ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this short communication is to illustrate the use of conditional maximization (CM) in chemometric applications. The CM algorithm is useful in reducing the computational complexity when a high-dimensional and complicated maximization problem arises from fitting chemometric models. It can also be efficiently combined with the expectation-maximization (EM) algorithm for handling incomplete data, a problem that sometimes arises when only a part of the intended data can be collected. Three models from fluorescence spectroscopy are used for illustration.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 423-437 
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    Keywords: Resolvability ; Evolutionary factor analysis ; Variable selection ; Window factor analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for selecting variables in the non-sequential direction of a two-way data matrix (e.g. wavelength in diode array HPLC) is described. Composition 1 and 2 resolvability indices are calculated according to the size of eigenvalues of uncentred data matrices as a window is moved along the sequential direction. A double-window technique is then performed where resolvability indices are calculated as a window is moved along the non-sequential direction. Some regions have higher resolvability indices and hence are more useful for resolution. Variables are ranked according to resolvability. Two simulations are analysed and it is shown that it is possible to obtain good resolution on a small subset of the original variables.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 45-63 
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    Keywords: GRAM ; GSVD ; Propagation of errorS ; Correlated noise ; Uncorrelated noise ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of correlated and uncorrelated random errors on the precision of predicted quantitative and qualitative information obtained by analysis with the generalized rank annihilation method (GRAM) are shown. These are discussed in terms of propagation of errors through the algorithm. The effects of colinearity, noise level and noise distribution are compared and discussed.
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    Journal of Chemometrics 8 (1994), S. 97-98 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 155-168 
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    Keywords: Trilinear models ; Tensorial resolution ; PARAFAC ; Swamps ; Two-factor degeneracy ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alternating least squares PARAFAC algorithm is a useful tool for resolving trilinear three-way data arrays. Occasionally, however, it becomes bogged down for many iterations in the vicinity of a poor quality resolution before moving on to a much superior optimum fit. We investigate this behavior in a simulation study and suggest ways of overcoming the obstacles it presents.
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    Journal of Chemometrics 8 (1994), S. 205-219 
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    Keywords: Fractional factorial design ; Significant effects ; ANOVA ; Probability plotting ; Bayes plot ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper presents a method for identifying significant effects in fractional factorial designs. The method is based on comparing functions of the estimated effects with a scale invariant reference distribution. The method is illustrated and compared with alternative techniques on a dataset from processed cheese production. The method corresponded well to other methods (probability plotting and Bayes plot) that do not make use of error estimates. These methods were better than F-tests with few (two or four) degrees of freedom for error.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 8 (1994), S. 245-261 
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    Keywords: Factor analysis ; Spectral resolution ; Two-dimensional luminescence ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A factor analysis algorithm that estimates the spectra of mixture components using the set of most dissimilar rows and/or columns is described and illustrated. This algorithm uses the distance as a measure of spectral similarity and is suitable for application to a variety of the bilinear matrix-formatted data types produced by hyphenated and multidimensional analytical techniqes. The algorithm requires that the data matrix contain at least one row or column that corresponds to the pure spectrum of each component to effect accurate spectral resolution. The performance of the method is illustrated using the resolution of excitation and emission spectra of up to four components from experimental fluorescence excitation-emission matrices (EEMs). In the case of the EEM, characteristic bands in an emission spectrum effect resolution of the excitation spectrum of the corresponding component, while characteristic bands in an excitation spectrum lead to resolution of the corresponding emission spectrum. The use of the set of most dissimilar rows and columns to evaluate the degree of overlap in the component spectra and compare the quality of row and column solutions is also described.
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  • 100
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 8 (1994), S. 293-294 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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