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  • 1
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    Bulletin of mathematical biology 50 (1988), S. 35-41 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A dynamical model of the left ventricle as a thick-walled cylinder contracting radially is used to derive the P-V (pressure-volume) relation in the left ventricular cavity during contraction. It is shown how the mathematical results derived could apply to experimental results.
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  • 2
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    Bulletin of mathematical biology 50 (1988), S. 67-75 
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    Notes: Abstract We give conditions for local and global stability of discrete one-dimensional population models. We give a new test for local stability when the derivative is −1. We give several sufficient conditions for global stability. We use these conditions to show that local and global stability coincide for the usual models from the literature and even for slightly more complicated models. We give population models, which are in some sense the simplest models, for which local and global stability do not coincide.
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  • 3
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    Bulletin of mathematical biology 50 (1988), S. 97-120 
    ISSN: 1522-9602
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    Notes: Abstract We consider efficient methods for computing a difference metric between two sequences of symbols, where the cost of an operation to insert or delete a block of symbols is a concave function of the block's length. Alternatively, sequences can be optimally aligned when gap penalties are a concave function of the gap length. Two algorithms based on the ‘candidate list paradigm’ first used by Waterman (1984) are presented. The first computes significantly more parsimonious candidate lists than Waterman's method. The second method refines the first to the point of guaranteeingO(N 2 lgN) worst-case time complexity, and under certain conditionsO(N 2). Experimental data show how various properties of the comparison problem affect the methods' relative performance. A number of extensions are discussed, among them a technique for constructing optimal alignments inO(N) space in expectation. This variation gives a practical method for comparing long amino sequences on a small computer.
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  • 4
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    Bulletin of mathematical biology 50 (1988), S. 187-192 
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    Notes: Abstract It is well documented, in the biological literature, that many species throughout the animal kingdom exhibit Gompertzian or Weibull-like population level total survival distributions. Many researchers have long assumed, believed, or otherwise postulated that an individual organism, in such a population, survived according to an exponential survival distribution. Using well-known results from reliability theory, it is shown that if every individual in the population has an exponentially distributed lifespan, then a Gompertzian or Weibull-like group/population level dynamics (or any other dynamics with a strictly increasing mortality rate for some interval) is not possible. This implies that, for species with a population level Gompertzian or Weibull (with the mortality rate strictly increasing) survival curve, some or all of the individual organisms must have non-exponentially distributed lifespans.
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  • 5
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    Bulletin of mathematical biology 50 (1988), S. 209-225 
    ISSN: 1522-9602
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    Notes: Abstract In flow cytometric measurement of cell DNA distribution one of the major problems is accounting for the effect of fragmentation in the staining process. This work considers a recent probabilistic model that has been proposed for the fragmentation process and species under which conditions it is possible to uniquely identify the DNA distributions of the original population using flow cytometric data. Attention is given both to the normal and to the polyploid case.
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  • 6
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    Bulletin of mathematical biology 50 (1988), S. 379-409 
    ISSN: 1522-9602
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    Notes: Abstract The nonlinear behavior of a particular Kolmogorov-type exploitation differential equation system assembled by May (1973,Stability and Complexity in Model Ecosystems, Princeton University Press) from predator and prey components developed by Leslie (1948,Biometrica 35, 213–245) and Holling (1973,Mem. Entomol. Soc. Can. 45, 1–60), respectively, is re-examined by means of the numerical bifurcation code AUTO 86 with model parameters chosen appropriately for a temperature dependent mite interaction on fruit trees. The most significant result of this analysis is that, in addition to the temperature ranges over which the single community equilibrium point of the system iseither globally stableor gives rise to a globally stable limit cycle, there can also exist a range wherein multiple stable states occur. These stable states consist of a focus (spiral point) and a limit cycle, separated from each other in the phase plane by an unstable limit cycle. The ecological implications of such metastability, hysteresis and threshold behavior for the occurrence of outbreaks, the persistence of oscillations, the resiliency of the system and the biological control of mite populations are discussed. It is further suggested that a model of this sort which possesses a single community equilibrium point may be more useful for representing outbreak phenomena, especially in the presence of oscillations, than the non-Kolmogorov predator-prey systems possessing three community equilibrium points, two of which are stable and the other a saddle point, traditionally employed for this purpose.
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    Bulletin of mathematical biology 50 (1988), S. 493-501 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract This note is concerned with a simple mathematical model of how a population of bacterial spores decrease with time when subjected to a uniform temperature. The model assumes that there is a Boltzman distribution of energy among water or other molecules surrounding the assumed single lethal target in a spore; it assumes that repair is not possible; and that only molecules with energies above a critical level cause inactivation. The model provides new insight concerning the ‘kill-rate’ of spores during ultra heat treatment.
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    Bulletin of mathematical biology 50 (1988), S. 95-95 
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  • 9
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    Bulletin of mathematical biology 50 (1988), S. 143-185 
    ISSN: 1522-9602
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    Notes: Abstract The kinetic theory of neural systems is extended to include the description of cortical-like neural structures. This fact is accomplished by the introduction of long-distance effects. Collaterally, we have the separation of the description of the excitatory activity from that of the inhibitory one. Also, the description of neural systems with a high level of activity is obtained. The modified theory is used to simulate computationally the activity of cortical-like neural systems.
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  • 10
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    Notes: Abstract A model based upon minimization of surface energy as an explanation for the phenomena of compaction and internalization of cells during mammalian embryo development is generalized for three-dimensional cells. It is shown that, for a spherical embryo, if cells are assumed to be polygonal cones in shape, the simulation of these phenomena for three-dimensional cells is equivalent to simulations of deformations of two-dimensional cells on the surface of a sphere. This equivalence is used to show that in the optimal compacted structure, with no internal cells, the cross-sections of cells in general are not regular polyhedra. Further, the internalization occurs when the number of cells exceeds a critical value which seems to depend on the relative sizes and biophysical properties of cells.
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    Bulletin of mathematical biology 50 (1988), S. 517-530 
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    Notes: Abstract In previous work (Freedman and Wolkowicz, 1986;Bull. math. Biol. 48, 493–508) it was shown that in a predator-prey system where the prey population exhibits group defence, it is possible that enrichment of the environment could lead to extinction of the predator population. In this paper a third population is introduced and criteria are derived under which persistence of all populations will occur. In particular, criteria for a superpredator and for a competitor to stabilize the system in the sense of persistence are analyzed.
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    Bulletin of mathematical biology 50 (1988), S. 531-545 
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    Notes: Abstract The interaction between osmotic inflow through the wall of a narrow tubule and bulk flow in the tubule is described. Solution are found by a finite difference method, and two approximate analytic solutions are given. Results given here enable more accurate estimates of osmotic permeability to be obtained for the tubule wall. The theory predicts the behaviour of unstirred layers as experimental parameters are varied and enables tubule experiments to be designed so as to reduce unwanted unstirred layer effects.
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    Bulletin of mathematical biology 50 (1988), S. 567-576 
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  • 14
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 635-660 
    ISSN: 1522-9602
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    Notes: Abstract Molecular evolution is modelled by erroneous replication of binary sequences. We show how the selection of two species of equal or almost equal selective value is influenced by its nearest neighbours in sequence space. In the case of perfect neutrality and sufficiently small error rates we find that the Hamming distance between the species determines selection. As the error rate increases the fitness parameters of neighbouring species become more and more important. In the case of almost neutral sequences we observe a critical replication accuracy at which a drastic change in the “quasispecies”, in the stationary mutant distribution occurs. Thus, in frequently mutating populations fitness turns out to be an ensemble property rather than an attribute of the individual. In addition we investigate the time dependence of the mean excess production as a function of initial conditions. Although it is optimized under most conditions, cases can be found which are characterized by decrease or non-monotonous change in mean excess productions.
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    Bulletin of mathematical biology 50 (1988), S. 681-696 
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    Notes: Abstract Time-dependent induction of clonal heterogeneity in the neoplastic micro-environment is analysed within the context of a competitive ecology. A model that describes a constant source for clonal emergence was analysed by Michelsonet al. (1987) as an extension of a model proposed by Jansson and Revesz (1974). The extended model has been termed the JRE Model. This paper extends these analyses to time-dependent emergence rates which may represent induction in the presence of a cytotoxic agent. If the analysis is constrained to the tumor micro-environment, and if the emergent subpopulation is drug resistant, then the model may describe the induction and emergence of drug resistant subclones in a growing neoplasm. Asymptotic closed form solutions are derived for a class of emergence rate functions which decay asymptotically to a constant mutation rate. This underlying mutation rate may represent spontaneous mutation to the resistant phenotype, and has been analysed stochastically (Coldmanet al., 1985). The asymptotic solutions to the time-dependent model approach the steady state solution for the JRE Model which represents the dynamics observed in the presence of a constant, spontaneous mutation rate. The clinical and biological implications of these results are discussed.
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    Bulletin of mathematical biology 50 (1988), S. 697-700 
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    Bulletin of mathematical biology 50 (1988), S. 701-701 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 345-349 
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    Notes: Abstract A simple scaling (semigroup) property is manifest in the functional form of the effective logistic rate for the increase in the HIV seropositive fraction in the San Francisco (City Clinic) cohort. Witht i=4.5 years, this scaling property—r→λ-2r undert→[λt+(λ−1)t i] for all parameter values λ≧1—encapsulates the effects of relevant biological and sociological changes in the key epidemiological variables during the 8-year seropositive rise period, 1978–1985 inclusive.
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    Bulletin of mathematical biology 50 (1988), S. 367-378 
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    Notes: Abstract Using plausible assumptions a description of the distribution of externally added low molecular weight solutes in individual subcellular regions of biosystems is reduced to a compartmental system of specific structure having, in general, only numerical solutions. Frequently occurring application of biologically active substances in low doses, however, elicits the conditions (i.e. undirectional membrane transport involving accumulation, instantaneous and linear binding to macromolecules and metabolism obeying first order kinetics) that enable one to solve the system explicitly. Equations have been derived, describing the time course of drug concentration in any subcellular phase of arbitrary biosystem having membranes of similar composition, including tissues with a cellular structure (degenerate case). Accuracy of the description is tested on the relationship between physicochemical and biological properties of drugs, bioactivity being used to monitor the concentration in the receptor region.
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    Bulletin of mathematical biology 50 (1988), S. 411-419 
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    Bulletin of mathematical biology 50 (1988), S. 547-558 
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    Notes: Abstract The influence of unstirred layers in osmotic experiments designed to measure the osmotic permeability of a tubule wall is considered. Results are given in the form of a set of graphs whose axes are closely related to observed and known experimental parameters. These enable osmotic permeability values to be obtained which are closer to the true values.
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    Bulletin of mathematical biology 50 (1988), S. 559-565 
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    Notes: Abstract In our previous paper we have given a neuroglia modulated neuronal network model which may display chaotic behaviours under certain parametric values. This work is an attempt to correlate the functions of conscious human brains with the chaotic states shown by the EEG patterns under different physiological conditions. Some of the difficulties and precautions of this kind of work are discussed.
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    Bulletin of mathematical biology 50 (1988), S. 577-577 
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    Bulletin of mathematical biology 50 (1988), S. 579-593 
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    Notes: Abstract By estimating relevant time scales, a simple new condition can be found that ensures the validity of the steady state assumption for a standard enzyme-substrate reaction. The generality of the approach is demonstrated by applying it to the determination of validity criteria for the steady state assumption applied to an enzyme-substrate-inhibitor system.
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    Notes: Abstract A simplified one-dimensional model system was used to test the possibility that physically realistic parameters would lead to the prediction of microscopic heterogeneity of radioligand distribution in the brain and that microscopic heterogeneity of radioligand and neuroreceptor distribution could influence the macroscopically observedin vivo kinetics. The model was represented mathematically by a partial differential equation which is similar to the heat diffusion equation, but with special boundary conditions. The equation was solved analytically under the condition of negligible receptor occupancy by inversion of the Laplace transform and in the more general case of arbitrary receptor occupancy by cubic spline approximation. In simulations with physically reasonable values for rate constants and parameters, we find that significant radioligand gradients can occur. Thus, the level of radioligand in the immediate vicinity of the receptor may be substantially different from the average level in a macroscopically measured region of interest. In order to analyze the simulated data, we derived a rigorous steady-state solution, including both a statement of necessary and sufficient conditions for the validity of the steady-state approximation as well as a demonstration of the proper technique for assessing the consistency of the derived parameter with the requirements of the approximation. The radioligand heterogeneity leads to significant errors in the parameters estimated in the steady-state kinetic analysis. In particular, the pseudo first-order rate constant for radioligand-neuroreceptor association, which is often used as a measure of the total amount of neuroreceptor, is underestimated. The first-order rate constant for radioligand-neuroreceptor dissociation is also underestimated. These effects can partially account for the experimentally-observed discrepancy betweenin vivo andin vitro estimates of these kinetic parameters.
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    Bulletin of mathematical biology 50 (1988), S. 595-634 
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    Notes: Abstract Many developing systems obey the principle of continuity: a morphogenetic field, when perturbed, tends to restore the normal local pattern of structures in its organ district. We have investigated physical field theories for a morphogenetic field, seeking constraints which would make a field theory produce the principle of continuity. We assume that during embryonic (ontogenetic) development a leg develops a pattern of positional values and a length which extremize a time-independent functional—the integral, over the length of the leg, of a function of positional values and position. For a single state variable which represents positional value, if a unique extremizing solution for the ontogenetically generated pattern and the length exists, and if no position-dependent functions other than the state variable appear in the integrand, then the principle of continuity is valid: in any regenerated leg the state variable is continuous and each region is locally identical to a region of the ontogenetically generated leg. This proposition is applied to three simple examples. For an exponential gradient and a Jacobi elliptic function there is a set of parameter values and boundary values for which a functional is minimized and the ontogenetically generated leg has an optimal length. Thus a leg which meets these constraints will obey the principle of continuity. However, a functional which when extremized gives a sinusoidal pattern does not in general provide a unique extremal length. Mathematical conditions are discussed under which an ontogenetically generated limb or a regenerated limb represents an asymptotically stable steady state. For a specific model of the transient dynamics in the exponential gradient case, the steady state gradient is asymptotically stable.
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    Bulletin of mathematical biology 50 (1988), S. 661-679 
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    Notes: Abstract Rhythmic “circa-second” contrations of larvae of the hornetVespa orientalis, believed to serve as hunger signals, were studied. A considerable degree of coordination among individual larvae, both in frequency and phase of these contractions, has been observed. The oscillations of singly isolated larvae are of short duration, non-constant, with increasing intervals in between and there is a substantial variability in the patterns shown by different larvae. In contrast, the association of two or more larvae leads to enhancement of their periodic behaviour and to (partial) entrainment. Communication among larvae may perhaps be mediated by the sound pulses (“scratching” noises) which are generated by these contractions. We have subjected individual and grouped larvae to external sound pulses and were able to demonstrate: (a) enhancement of rhythmic activity; (b) phase resetting; (c) entrainment to an external oscillator within a range of frequencies; (d) the existence of a subharmonic mode of entrainment. We propose a simple phenomenologic model to account for these larvae responses. Our model assumes the existence of an “energy” variable which declines with time but is upgraded, in a phase-dependent way, by external stimuli.
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    Bulletin of mathematical biology 50 (1988), S. i 
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    Bulletin of mathematical biology 50 (1988), S. 1-17 
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    Notes: Abstract Multiple solutions of a model describing immune surveillance against cancer are studied. The model was proposed by R. Lefever and co-workers. A limit cycle solution and two kinds of wave front solutions are worked out by means of a perturbation method. The problem of nucleation concerning this model is studied by a singular-perturbation technique. In addition, the pulse wave solution is also found by numerical simulations.
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    Bulletin of mathematical biology 50 (1988), S. 19-34 
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    Notes: Abstract It is productive to view the suture-lines on fossil cephalopod shells as simple Fraunhoeffer diffraction patterns which can be inverted, by elementary Fourier Transformation, to provide a clear holographic image of the soft body-mass that produced them. As fleshy body organs are rarely ever preserved in ancient fossils it is particularly valuable to be able to deduce soft anatomy from conspicuous and usually well-preserved shell markings. Preliminary studies reported in this paper supply insight into the ontogeny and phylogeny of ancient cephalopods.
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    Bulletin of mathematical biology 50 (1988), S. 43-66 
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    Notes: Abstract This paper is concerned with a population of neurons with dense random interconnections, in which the stimulations between neurons are independent of their distance apart. This study is conducted from the viewpoint of the General System Theory. Proposed and used for the first time in studies on the above subject is a new concept referred to as the ‘historical report’ of the mentioned population. It will be shown that the population exhibits cyclic modes of behaviour which are dependent on its structure and historical report and which in the phase space correspond to cycles of hysteresis. A simple model in discrete time is developed and demonstrates, by the help of a computer study, the existence of the cycles of hysteresis.
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    Bulletin of mathematical biology 50 (1988), S. 77-92 
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    Notes: Abstract A class of non-linear similarity functionss 1 has been proposed for comparing subalignments of biological sequences. The distribution of maximals 1-similarities is well approximated by the extreme value distribution. The significance levels ofs 1 are studied for a variety of nucleotide frequency distributions as well as for several matrices of amino acid substitution costs. Also, the significance levels ofs 1 are explored for comparing three biological sequences. Several previously described subalignments of bovine proenkephalin and porcine prodynorphin are shown to be highly significant.
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 193-207 
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    Bulletin of mathematical biology 50 (1988), S. 289-311 
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    Notes: Abstract A mathematical model of capillary-tissue exchange is presented and the method of solution of the resulting equations is described. The model includes the mutual interaction of fluid movement across the capillary wall and the convection and diffusion of a number of solutes. A variety of solutions for situations of physiological interest are obtained and discussed.
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    Bulletin of mathematical biology 50 (1988), S. 255-288 
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    Notes: Abstract A theory is presented for appearance of periodic band patterns of ion concentration and electric potential associated with electric current surrounding a unicellular or multicellular system of a cylindrical shape. A flux continuity at the membrane (or the surface) is reduced to a nonlinear equation expressing passive and active fluxes across the membrane and intracellular diffusion flux. It is shown that, when an external parameter is varied from the sub-critical region, i.e. the homogeneous flux state, a symmetry breaking along a longitudinal axis usually appears prior to the one along a circumferential direction. The spectrum analysis shows that the correlation length is longer in the longitudinal direction. Growth of the band pattern from a patch-shaped pattern is demonstrated by the use of numerical calculations of proton concentration on the two-dimensional space of cylindrical surface. An experimental example of formative process of H+ banding is given for the internodal cell ofChara. It is shown that small patches on the surface decline or are sometimes gathered to the band surrounding the circle. The resulting pattern is suggested as a kind of dissipative structure appearing far from equilibrium.
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    Bulletin of mathematical biology 50 (1988), S. 227-253 
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    Notes: Abstract Many theoretical studies in biological and physical sciences consider the dynamical behavior of ann-dimensional ordinary differential equation that contains a large number of independent parameters. A frequently asked question is, are there permissible parameter sets that result in periodic or chaotic behavior? The large number of distinct parameters often limits the feasibility of trial and error calculations. The large dimension and nonlinearity of the system make application of analytic methods at best difficult and at worst effectively impossible. It is shown here that a computational search for parameter-dependent transitions of attractor topology can be effected by constrained optimization of quantitative measures of dynamical behavior (Hurwitz polynomials, Floquet coefficients, Lyapunov exponents and correlation dimension). As an example, we examine a three-dimensional nonlinear ordinary differential equation containing seven parameters that was constructed by Goldbeter and Segel to model periodic synthesis of cyclic AMP inDictyostelium. A search for bifurcations to periodic solutions is made by minimizing Hurwitz coefficients subject to parameter constraints. By comparing four optimization algorithms, the defects and advantages of the procedure are identified. It is also argued that it may be possible to use this characterization of dynamics to construct optimal responses to dynamical diseases (those disorders that result from parameter-dependent bifurcations in physiological control systems).
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    Bulletin of mathematical biology 50 (1988), S. 351-366 
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    Notes: Abstract Survival analyses of populations are developed in dicrete growth processes. Persistence and extinction attributes of age-structured discrete population models are explored on both a finite and infinite time horizon. Conditions for persistence and extinction are found. Decompositions of the initial population size axes into intervals where populations are persistent at timeN and intervals leading to extinction at timen, wheren≤N, are given for two age class discrete population models.
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    Bulletin of mathematical biology 50 (1988), S. 329-344 
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    Notes: Abstract A simple mathematical model depicting blood flow in the capillary is developed with an emphasis on the permeability property of the blood vessel based on Starling's hypothesis. In this study the effect of inertia has been neglected in comparison with the viscosity on the basis of the smallness of the Reynolds number of the flow in the capillary. The capillary blood vessel is approximated by a circular cylindrical tube with a permeable wall. The blood is represented by a couple stress fluid. With such an ideal model the velocity and pressure fields are determined. It is shown that an increase in the couple stress parameter increases the resistance to the flow and thereby decreases the volume rate flow. A comparison of the results with those of the Newtonian case has also been made.
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    Bulletin of mathematical biology 50 (1988), S. 421-422 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 445-464 
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    Notes: Abstract Adaptation is viewed as a tendency maximizing the Shannon entropy of an ecosystem, where the ecosystem is considered as two interacting subsystems, namely, the biota and its environment. We derive theadapted structures starting from three fundamental hypotheses and we apply this result to an ecological topic: the cryptic and aposematic behaviour.
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    Bulletin of mathematical biology 50 (1988), S. 465-491 
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    Notes: Abstract The behavior of a model that generalizes the Lotka-Volterra problem into three dimensions is presented. The results show the analytic derivation of stability diagrams that describe the system's qualitative features. In particular, we show that for a certain value of the bifurcation parameter the system instantly jumps out of a steady state solution into a chaotic solution that portrays a fractal torus in the three-dimensional phase space. This scenario, is referred to as the explosive route to chaos and is attributed to the non-transversal saddle connection type bifurcation. The stability diagrams also present a region in which the Hopf type bifurcation leads to periodic and chaotic solutions. In addition, the bifurcation diagrams reveal a qualitative similarity to the data obtained in the Texas and Bordeaux experiments on the Belousov-Zhabotinskii chemical reaction. The paper is concluded by showing that the model can be useful for representing dynamics associated with biological and chemical phenomena.
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    Bulletin of mathematical biology 50 (1988), S. 503-515 
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    Notes: Abstract Traditional population models describe changes in population size as a function of changes in the resources. Such first-order models cannot describe certain properties of population dynamics. General models with delays can account for all the observed dynamic complexities but are judged overgeneralized. It is proposed that the simplest model of intermediate complexity that explains such dynamic properties is a second-order model, which describes population dynamics as a function of a physiological variable, the dynamics of which in turn depends on resources. Data on accelerated decline of populations in the absence of food from experiments with brown and green hydra as well as literature data support the arguments.
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 313-328 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Mathematical programming 42 (1988), S. 363-374 
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    Keywords: Newton method ; parallel algorithms ; superlinear convergence
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    Notes: Abstract A parallel Newton method is described for the minimization of a twice continuously differentiable uniformly convex functionF(x). The algorithm generates a sequence {x j } which converges superlinearly to the global minimizer ofF(x).
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    Mathematical programming 42 (1988), S. 489-563 
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    Notes: Abstract Polyhedra related to matroids and sub- or supermodular functions play a central role in combinatorial optimization. The purpose of this paper is to present a unified treatment of the subject. The structure of generalized polymatroids and submodular flow systems is discussed in detail along with their close interrelation. In addition to providing several applications, we summarize many known results within this general framework.
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    Mathematical programming 42 (1988), S. 113-123 
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    Keywords: Scheduling ; large-scale 0–1 model ; variable fixing ; coefficient reduction ; special ordered sets
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    Notes: Abstract In this work an extension of the Beale-Tomlin special ordered sets is introduced that has proved to be efficient for solving certain types of open shop scheduling problems. Besides their usual characteristics, exclusivity constraints in the jobs are allowed, more general than tree-like precedence structures are considered, and semi-active schedules that cannot be labeled as non-optimal solutions may occur. The problem is formulated as a large-scale 0–1 model. Computational experience on some real-life problems is reported.
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    Mathematical programming 42 (1988), S. 181-187 
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    Keywords: Branch and bound ; bus crew scheduling ; integer programming ; scheduling ; set covering
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    Mathematical programming 42 (1988), S. 203-243 
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    Keywords: Network flows ; relaxation ; distributed algorithms ; complexity ; asynchronous algorithms
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    Notes: Abstract We review a class of recently-proposed linear-cost network flow methods which are amenable to distributed implementation. All the methods in the class use the notion ofε-complementary slackness, and most do not explicitly manipulate any “global” objects such as paths, trees, or cuts. Interestingly, these methods have stimulated a large number of newserial computational complexity results. We develop the basic theory of these methods and present two specific methods, theε-relaxation algorithm for the minimum-cost flow problem, and theauction algorithm for the assignment problem. We show how to implement these methods with serial complexities of O(N 3 logNC) and O(NA logNC), respectively. We also discuss practical implementation issues and computational experience to date. Finally, we show how to implementε-relaxation in a completely asynchronous, “chaotic” environment in which some processors compute faster than others, some processors communicate faster than others, and there can be arbitrarily large communication delays.
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    Mathematical programming 42 (1988), S. 307-325 
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    Keywords: Full discretization ; computerized tomography ; image reconstruction ; radiotherapy treatment planning ; block-iterative algorithms ; parallel computations ; Cimmino's algorithm ; entropy maximization ; classification of algorithms
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    Notes: Abstract Some row-action algorithms which exploit special objective function and constraints structure have proven advantageous for solving huge and sparse feasibility or optimization problems. Recently developed block-iterative versions of such special-purpose methods enable parallel computation when the underlying problem is appropriately decomposed. This opens the door for parallel computation in image reconstruction problems of computerized tomography and in the inverse problem of radiation therapy treatment planning, all in their fully discretized modelling approach. Since there is more than one way of deriving block-iterative versions of any row-action method, the choice has to be made with reference to the underlying real-world problem.
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    Mathematical programming 42 (1988), S. 391-405 
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    Keywords: Linear programming ; large-scale-systems ; decomposition ; parallel computing
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    Notes: Abstract This paper describes DECOMPAR: an implementation of the Dantzig-Wolfe decomposition algorithm for block-angular linear programs using parallel processing of the subproblems. The software is based on a robust experimental code for LP decomposition and runs on the CRYSTAL multicomputer at the University of Wisconsin-Madison. Initial computational experience is reported. Promising directions in future development of this approach are discussed.
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    Mathematical programming 42 (1988), S. 471-487 
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    Notes: Abstract We address the problem of finding a minimum weight baseB of a matroid when, in addition, each element of the matroid is colored with one ofm colors and there are upper and lower bound restrictions on the number of elements ofB with colori, fori = 1, 2,⋯,m. This problem is a special case of matroid intersection. We present an algorithm that exploits the special structure, and we apply it to two optimization problems on graphs. When applied to the weighted bipartite matching problem, our algorithm has complexity O(|E∥V|+|V| 2log|V|). HereV denotes the node set of the underlying bipartite graph, andE denotes its edge set. The second application is defined on a general connected graphG = (V,E) whose edges have a weight and a color. One seeks a minimum weight spanning tree with upper and lower bound restrictions on the number of edges with colori in the tree, for eachi. Our algorithm for this problem has complexity O(|E∥V|+m 2 |V|+ m|V| 2). A special case of this constrained spanning tree problem occurs whenV * is a set of pairwise nonadjacent nodes ofG. One must find a minimum weight spanning tree with upper and lower bound restrictions on the degree of each node ofV *. Then the complexity of our algorithm is O(|V∥E|+|V * ∥V| 2). Finally, we discuss a new relaxation of the traveling salesman problem.
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    Monatshefte für Mathematik 106 (1988), S. 1-8 
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    Notes: Abstract IfK is an equichordal set of chord length 1, i.e. ann-dimensional convex body with a pointp εK such that every chord throughp has length 1, it can be shown that ω n /2 n ⩽v(K) 〈 ω n /2, wherev(K) denotes the volume ofK and ω n the volume of ann-dimensional unit ball. Explicit estimates are established for the deviation ofK from a ball of radius 1/2 ifv(K)−ω n /2 n is small, and from a semiball of radius 1 if 1/2ω n −v(K) is small.
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    Monatshefte für Mathematik 106 (1988), S. 25-40 
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    Notes: Abstract In this paper we prove bounded laws of the iterated logarithm for Gaussian quadratic forms. The underlying sequence of Gaussian variables is assumed to satisfy quite general conditions on its covariance structure. Basic tools are maximal inequalities of exponential type for sums of dependent random variables which may be of own interest. Several examples illustrate the sharpness of the results. In a particular section the bounded law of the iterated logarithm is shown for quadratic variation of Brownian motion.
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    Monatshefte für Mathematik 106 (1988), S. 9-23 
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    Notes: Abstract The information comparison ℰ A 〉ℰ B between two linear normal experiments ℰ A , ℰ B is studied in terms of the Loewner orderingA≤B between their defining design matricesA, B respectively. The result due toKiefer [3],Takeuchi [5]Hansen, Torgersen [1] and others is related to the comparison of certain translation invariant experiments via a reduction principle. The analysis given here completes the discussion in § 25 of [2].
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    Monatshefte für Mathematik 106 (1988), S. 41-56 
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    Notes: Abstract In this paper, Rédeifunctions over residue class ringsZ/(m) are studied. In contrast to earlier investigations, now the modulusm is an arbitrary natural number 〉1, and the Rédei-functions are defined in dependence of a quadratic polynomial of the general formt(x)=x 2 −αx−β, t (x) irreducible modulo all prime divisorsp i ofm. A necessary and sufficient condition is formulated that a given Rédei-function induces a permutation ofZ/(m). Given a polynomialt(x), the group structure of the corresponding Rédei-permutations is determined.
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    Monatshefte für Mathematik 106 (1988), S. 95-97 
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    Notes: Abstract We give another proof of Seymour and Zaslavsky's theorem: For every familyf 1,f 2,...,f n of continous functions defined on [0, 1], there exists a finite setF⊂[0, 1] such that the average sum off k overF coincides with the integral off k for everyk=1, 2,...,n.
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    Monatshefte für Mathematik 106 (1988), S. 107-114 
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    Notes: Abstract A new stability property of the densest circle packing in the plane is proved. This property is related to a conjecture ofL. Fejes Tóth.
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    Monatshefte für Mathematik 106 (1988), S. 99-105 
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    Notes: Abstract J 3 (1) . Bonnet's classical theorem about ruled surfaces in the three-dimensional Euclidean space does not hold inJ 3 (1) . To get an isotropic version of this theorem the terms “geodetic line” and “isogonal-trajectory of the generators” are replaced by new, the isotropic space adapted properties of curves on ruled surfaces.
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    Monatshefte für Mathematik 106 (1988), S. 115-138 
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    Notes: Abstract We show how are located the positive roots of the Euler polynomiale n of degreen. We give an upper bound and a lower bound for the greatest root. This permits to determine an integerv (n) such that the number of positive roots ofE n is eitherv (n) orv (n) +2. We also study the behaviour of ther-th positive root ofE n asn tends to infinity.
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    Monatshefte für Mathematik 106 (1988), S. 139-148 
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    Notes: Abstract LetB(H) denote the algebra of operators on the Hilbert spaceH into itself. GivenA,BεB(H), defineC (A, B) andR (A, B):B(H)→B(H) byC (A, B) X=AX−XB andR(A, B) X=AXB−X. Our purpose in this note is a twofold one. we show firstly that ifA andB *εB (H) are dominant operators such that the pure part ofB has non-trivial kernel, thenC n (A, B) X=0, n some natural number, implies thatC (A, B)X=C(A *,B *)X=0. Secondly, it is shown that ifA andB * are contractions withC 0 completely non-unitary parts, thenR n (A, B) X=0 for some natural numbern implies thatR (A, B) X=R (A *,B *)X=C (A, B *)X=C (A *,B) X=0. In the particular case in whichX is of the Hilbert—Schmidt class, it is shown that his result extends to all contractionsA andB.
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    Monatshefte für Mathematik 106 (1988), S. 149-159 
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    Notes: Abstract Statistical independence properties of recently proposed nonlinear congruential pseudorandom number generators are analyzed by means of the serial test. The results that are established are essentially best possible. The method relies heavily on bounds for exponential sums.
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    Monatshefte für Mathematik 106 (1988), S. 161-170 
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    Monatshefte für Mathematik 106 (1988), S. 205-210 
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    Notes: Abstract In this paper we will characterize all subsemigroups of finitely generated abelian groups, for which there exists a divisor-theory. Besides an explicit geometrical construction of the divisor-theory is given, and it is shown that any finitely generated abelian group occurs as the divisor-class-group of some semigroup.
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    Monatshefte für Mathematik 106 (1988), S. 179-204 
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    Notes: Abstract LetS be an open subsemigroup of a Lie groupG with $$1 \in \bar S$$ . We shall show that for every congruence ℋ onS with closed congruence classes there exists an open neighborhoodU of1 inG and a foliation ofS ∩U whose leaves locally coincide with both the congruence classes of ℋ and the cosets of a normal analytic subgroup ofG which is uniquely determined by ℋ.
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    Monatshefte für Mathematik 106 (1988), S. 171-178 
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    Notes: Abstract LetG be a finite group. By a rational coefficient system forG we mean a contravariant functor from the category of canonical orbits ofG andG-maps into the category of ℚ-vector spaces. In this paper we study injective objects in the category of rational coefficient systems forG.
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    Monatshefte für Mathematik 106 (1988), S. 245-256 
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    Monatshefte für Mathematik 106 (1988), S. 221-244 
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    Notes: Abstract The cohomology of various sheaves associated with a Lagrangian foliation is discussed. Obstructions for the foliation either to behave like in the case of a cotangent bundle or to have an affine transversal distribution are found in this cohomology. Furthermore, one proves a formula for all the symplectic structures of a cotangent bundle such that the fibers constitute a Lagrangian foliation.
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    Monatshefte für Mathematik 106 (1988), S. 257-264 
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    Notes: Abstract We obtain some new formulas for convex hypersurfaces in a space form.
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    Monatshefte für Mathematik 106 (1988), S. 265-299 
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    Notes: Abstract It is shown that the affine plane over the Cayley numbers is the only 16-dimensional locally compact topological translation plane having a collineation group of dimension at least 41. This (hitherto unpublished) result is one of the ingredients of H. Salzmann's characterizations of the Cayley plane among general compact projective planes by the size of its collineation group. The proof involves various case studies of the possibilities for the structure and size of collineation groups of 16-dimensional locally compact translation planes. At the same time, these case studies are important steps for a classification program aiming at the explicit determination of all such translation planes having a collineation group of dimension at least 38.
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    Monatshefte für Mathematik 106 (1988), S. 301-312 
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    Notes: Abstract We endow the set of all invariant measures of topologically transitive subsetsL withh top (L)〉0 of a continuous piecewise monotonic transformation on [0, 1] with the weak topology. We show that the set of periodic orbit measures is dense, that the sets of ergodic, of nonatomic, and of measures with supportL are denseG δ-sets, that the set of strongly mixing measures is of first category, and that the set of measures with zero entropy contains a denseG δ-set.
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    Monatshefte für Mathematik 106 (1988), S. 337-347 
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    OR spectrum 10 (1988), S. 28-28 
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    Topics: Mathematics , Economics
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    OR spectrum 10 (1988), S. 1-12 
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    Description / Table of Contents: Summary Often statistical data are available only in grouped form. In this paper we give a survey on estimation of parameters from grouped data using the Maximum-Likelihood-Method. First some notation is introduced and it is shown how the loss of information due to grouping may be quantified. The stochastic properties of Maximum-Likelihood-Estimates and various methods for their computation are discussed. Finally some empirical examples are given.
    Notes: Zusammenfassung Statistische Daten sind oft nur in gruppierter Form verfügbar. In dieser Arbeit wird ein Überblick über die Maximum-Likelihood-Methode zur Parameterschätzung aus gruppierten Daten gegeben. Nach Einführung der Notation wird gezeigt, wie der Informationsverlust, der durch die Gruppierung entsteht, quantifiziert werden kann. Die stochastischen Eigenschaften der Maximum-Likelihood-Schätzer werden behandelt. Ausführlich wird auf verschiedene Methoden zur Berechnung der Maximum-Likelihood-Schätzwerte eingegangen. Einige empirische Beispiele schließen die Arbeit ab.
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    OR spectrum 10 (1988), S. 13-22 
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    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Für unendlich-stufige diskontierte Markovsche Entscheidungsprozesse werden Bedingungen angegeben, unter denen sogenannte “diskont-isotone” optimale Politiken existieren. Eine diskont-isotone Familie von optimalen Politiken liegt vor, wenn die Zustands- und Aktionenräume halbgeordnet sind und für eine Menge von Diskontierungsfaktoren je eine optimale Politik existiert, so daß in jedem Zustand die optimalen Aktionen isoton vom Diskontierungsfaktor abhängen. Es kann günstiger sein, zunächst Probleme mit kleinem Diskontierungsfaktor zu lösen und dann die Isotonie-Eigenschaften zur Lösung für größere Diskontierungsfaktoren heranzuziehen.
    Notes: Summary This paper considers infinite horizon discounted Markov decision processes and conditions under which discount-isotone optimal policies exist. Given partial orders over the state and action spaces, a set of discount-isotone optimal policies is a set of optimal policies, one for each discount factor in a given set, such that, for each state, the optimal actions are partially ordered in such a manner as to match the ordering of the discount factors. It is easier to solve problems with small discount factors and the induced partial ordering facilitates the solutions for higher discount factor levels.
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    OR spectrum 10 (1988), S. 36-36 
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  • 83
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    Description / Table of Contents: Zusammenfassung Der vorliegende Artikel behandelt einen expliziten Kostenausdruck für eine stetige Überprüfung der (S, s) Bestellpolitik eines Lagerhaltungssystems verderblicher Güter im stationären Fall. Der Kostenausdruck ist eng verbunden mit der stationären Verteilung des stochastischen ProzessesL(t), der den Lagerbestand zu jeder beliebigen Zeitt darstellt. Das stochastische Verhalten des Prozesses {L(t),t≳-0} wird characterisiert durch die Identifikation eines eingebetteten MRP. Die Nachfragewerte des Systems werden durch einen Poisson-Prozeß bestimmt. Die gelagerten Güter haben eine nutzbare Lebensdauer, die durch eine Erlang-Verteilung beschrieben wird. Die Durchlaufzeit ist eine Zufallsvariable mit spezifierter Wahrscheinlichkeitsverteilung. Es wird zudem unterstellt, daß nicht befriedigte Nachfrage bei leerem Lager verloren geht.
    Notes: Summary This article obtains an explicit cost expression for a continuous review (S, s) ordering policy inventory system of perishable items, in the stationary case. The cost expression is closely related to the stationary distribution of the stochastic processL(t), representing the inventory at any timet. The stochastic behaviour of the process {L(t),t≳-0} is characterised by identifying an imbedded MRP. The demands of the system are governed by a Poisson process. The items in the inventory have a useful life time characterised by an Erlangian distribution. The lead time is a random variable with specified probability distribution. It is assumed that the demands that arrive when the inventory is zero are lost.
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    OR spectrum 10 (1988), S. 29-35 
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    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Wir geben einen Überblick über verschiedene Methoden für nicht konvexe Minimisierungsaufgaben. Insbesondere diskutieren wir Aufzählungsmethoden für Extrempunkte. Wir betrachten konkave, quadratisch indefinite Probleme ebenso wie Probleme spezieller Struktur: konkave Netzwerk-Fluß-Probleme und lineare Komplementaritäts-Probleme. Wir schlagen neue Methoden vor, um lineare untere Schranken für Aufzählungstechnicken zu erhalten.
    Notes: Summary We give an overview on different methods for solving nonconvex minimization problems using techniques of enumeration of extreme points. The problems considered include concave, indefinite quadratic, and special structured problems such as the concave cost network flow problem and linear complementarity. For methods that enumerate the extreme points according to the ascending order of the value of a linear underestimating function we propose new techniques for obtaining such underestimators.
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    OR spectrum 10 (1988), S. 54-54 
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  • 86
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    OR spectrum 10 (1988), S. 54-54 
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    OR spectrum 10 (1988), S. 45-53 
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    Description / Table of Contents: Zusammenfassung Ein mathematisches Modell zur Berechnung der Entladezeit und Optimierung der Entlade-Strategie für mit Schüttgut beladene Schiffe ist zu entwickeln. Als erster Schritt wird in diesem Artikel der Entladevorgang einer einzigen Luke (Schiffs-Ladekammer) analysiert und durch ein mathematisches Modell beschrieben. Das Modell ermöglicht es dem Anwender, die Entladezeit einer Luke für beliebige Entlade-Dispositionen rechnerisch zu bestimmen und somit verschiedene Dispoitionen miteinander zu vergleichen.
    Notes: Summary A mathematical model for computation of unloading time and optimization of unloading strategy for ships transporting bulk goods is searched for. As the first step the unloading process of a single hatch (ship's freight room) is analysed and described by a mathematical model in this paper. The model essentially enables one to compute the unloading time of a hatch for any given unloading procedure and thus to compare and value different competing procedures.
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    OR spectrum 10 (1988), S. 37-44 
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    Description / Table of Contents: Zusammenfassung Der Zusammenhang zwischen den grundlegenden Bedienungscharakteristiken eines Schnellimbißkiosks und dem Verhalten seiner Kunden wird anhand eines Modells untersucht, welches den Lernprozeß der wartenden Kunden in bezug auf die Bedienungszeit in Rechnung stellt. Das Modell ist auf zwei Fälle ausgelegt. Im ersten Fall wird ein Kiosk in einem Einkaufskomplex betrachtet, dessen Kunden unsicher über die Bedienrate sind. Der zweite Fall behandelt einen Kiosk in einem Bürokomplex, wobei die Kunden Vorinformationen über die Bedienrate besitzen. Simulationsexperimente mit dem Modell offenbaren, wie die Unterschiede zwischen der erwarteten (oder versprochenen) und der beobachteten (oder geleisteten) Bediengeschwindigkeit und -qualität den Verlust von Kundschaft verursachen, bei zwei hypothetischen sowie zwei realen Schnellimbissen.
    Notes: Summary The relationship between a fast-food kiosk's basic operating characteristics and its customers' behavior is examined using a model which takes into account the learning process of the waiting customers with respect to the service time. The model is adapted to two cases. In the first case, a kiosk in a shopping complex is considered, whose customers are uncertain about the service rate. The second case deals with a kiosk in an office complex and its customers have prior information about the service rate. Simulation experiments with the model reveal how the discrepancies between the expected (or promised) and perceived (or delivered) service speed and quality cause lost patronage at two hypothetical and two real world fast-food operations.
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    OR spectrum 10 (1988), S. 64-64 
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    OR spectrum 10 (1988), S. 185-185 
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    OR spectrum 10 (1988), S. 173-183 
    ISSN: 1436-6304
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    Topics: Mathematics , Economics
    Description / Table of Contents: Summary The innovation problem of a single firm is described as a sequential decision problem under uncertainty. In each period the firm can improve its technology by R&D activities. It is shown that a “reservation technology” exists — the firm stops its efforts in R&D before reaching the technological limit. The reservation technology can be influenced by competition or basic research. Moreover, new insights into the innovation advantages of big corporations are given.
    Notes: Zusammenfassung Das Innovationsproblem einer Firma wird im Rahmen eines sequentiellen Entscheidungsproblems bei Unsicherheit behandelt. Dabei kann die Firma unter Aufwendung von F&E-Ausgaben in jeder Periode ihr bisheriges Technologieniveau/ihre bisherige Produktqualität verbessern. Unter plausiblen Annahmen kann gezeigt werden, daß ein „Reservationstechnologieniveau“ existiert, ab dem es für eine Firma nicht mehr lohnend ist, F&E zu betreiben. Innovationskonkurrenz bzw. Grundlagenforschung können diese kritische Grenze positiv beeinflussen. Ein neues, interessantes Ergebnis über den Zusammenhang zwischen Firmengröße und Innovationsaktivität wird demonstriert.
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  • 92
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  • 93
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    Description / Table of Contents: Zusammenfassung Eines der Probleme, die beim Gestaltungsprozeß elektromechanischer Vermittlungseinheiten auftreten, besteht darin, viele untereinander verbundene Objekte auf Positionen anzuordnen, die eine gegebene Struktur bilden. In diesem Papier wird beschrieben, wie dieses Problem mit Plazierungs- und Reihenfolgeheuristiken gelöst werden kann. Das reale Problem wird kurz angesprochen und die Optimierungs-probleme werden formal dargestellt. Zwei verschiedene Ansätze für ihre Lösung werden vorgestellt und unter Berücksichtigung ihres Rechenaufwands diskutiert. Zusätzlich werden einige erläuternde Beispiele von verbesserten Gestaltungen gegeben.
    Notes: Summary One problem in the design of electromechanical exchange units consists in arranging a large number of interconnected objects in positions forming a given structure. We describe in the present paper how this problem can be solved with placement and routing heuristics. The real-life problem is briefly reported and the optimization problems are stated formally. Two different approaches to their solution are presented and discussed with reference to the computational effort required for each. Some illustrative examples of improved designs are also given.
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    OR spectrum 10 (1988), S. 221-235 
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    Description / Table of Contents: Summary We consider a health programme from a policy perspective. This programme is specified for certain subgroups of a population, which can be treated in varying intensities. Its effectiveness depends on resources spent. We take into account that several resource categories may exist. The group-specific subproblems are modelled as stochastic decision chains with continuous action space, piecewise linear, monotone, convex cost functions and finite horizon. This paper develops a LP-model for efficient, simultaneous resource allocation.
    Notes: Zusammenfassung Im Rahmen strategischer Überlegungen kann ein Gesundheitsprogramm für verschiedene Untergruppen einer Population jeweils spezifisch ausgelegt und unterschiedlich intensiv betrieben werden. Programmintensität und -Wirksamkeit hängen vom Ressourceneinsatz ab. Hier werden mehrere Ressourcenkategorien zugelassen, und die untergruppenspezifischen Teilprogramme werden als stochastische Entscheidungsketten mit stetigem Aktionsraum, stückweise linearen, monotonen, konvexen Kostenfunktionen und endlichem Horizont modelliert. Wir entwickeln ein LP-Modell, das die effiziente Simultanallokation der Ressourcen zum Ziel hat.
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    OR spectrum 10 (1988), S. 236-236 
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    OR spectrum 10 (1988), S. 195-212 
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    Description / Table of Contents: Zusammenfassung „Extrapolative“ Zeitreihenprognoseverfahren sind in der betriebswirtschaftlichen Praxis weit verbreitet. Ihre große praktische Bedeutung hat nicht nur zur Entwicklung neuer Prognoseverfahren geführt, sondern auch zu vergleichenden Untersuchungen und Beurteilungen etablierter Methoden. Dieser Beitrag stellt eine Übersicht der wichtigsten „extrapolativen“ Prognoseverfahren dar. Darüberhinaus befaßt er sich mit neueren Untersuchungen zur relativen Genauigkeit dieser Verfahren und unterstreicht die teilweise unerwarteten Schlußfolgerungen dieser neuen Untersuchungen. Unternehmen sind daran interessiert, daß für sie am besten geeignete Prognoseverfahren zu wählen. Der Beitrag erörtert die Art des Wahlprozesses und bespricht die Frage, inwieweit Zeitreihenmethoden betriebswirtschaftliche Urteile ergänzen können. Zum Schluß befaßt sich der Beitrag kurz mit Prognoseverfahren Software und äußert eine persönliche Meinung über Zeitreihenprognoseverfahren.
    Notes: Summary Time series (extrapolative) forecasting procedures are widely used in business. Their importance has led to the development of new methods of forecasting and research into the evaluation of well-established methods. This paper presents an overview of the major methods of extrapolative forecasting. Secondly it considers the evidence on the relative accuracy of these methods, highlighting the unexpected conclusions arrived at by this new research. Organizations need to identify the forecasting method most appropriate to their particular circumstances. The paper discusses how such a selection should take place, commenting on how time series methods can complement managerial judgement. The paper concludes with some brief remarks on forecasting software, and a personal view of the future of time series forecasting.
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    OR spectrum 10 (1988), S. 248-248 
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    OR spectrum 10 (1988), S. 249-249 
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    OR spectrum 10 (1988), S. 250-250 
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    OR spectrum 10 (1988), S. 237-247 
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    Description / Table of Contents: Summary In order to make the German market for software on cutting stock problems more transparent suppliers of computer programs are assembled and asked on the basis of a detailed catalogue of criteria developed before. The paper documents this empirical investigation and presents the results for 28 programs of 14 different firms.
    Notes: Zusammenfassung Um auf dem unübersichtlichen Softwaremarkt das Angebot an Standardsoftware zur DV-mäßigen Unterstützung und Optimierung industrieller Zuschneideprozesse transparenter zu gestalten, wurden Anbieter entsprechender Programme erhoben und auf der Basis eines zuvor entwickelten Kriterienkatalogs befragt. Der Beitrag dokumentiert diese empirische Untersuchung und stellt als Ergebnis 28 Programme von 14 verschiedenen Anbietern vergleichend gegenüber.
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