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  • Springer  (131,078)
  • American Meteorological Society
  • 1995-1999  (67,377)
  • 1990-1994  (62,371)
  • 1940-1944  (4,122)
  • 1998  (67,377)
  • 1991  (62,371)
  • 1941  (4,122)
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  • 1995-1999  (67,377)
  • 1990-1994  (62,371)
  • 1940-1944  (4,122)
Year
  • 1
    Electronic Resource
    Electronic Resource
    The economics of exhaustible resources (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 281-312 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464433
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  • 2
    Electronic Resource
    Electronic Resource
    Some aspects of the dynamics of populations important to the management of the commercial Marine fisheries (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 253-279 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464432
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  • 3
    Electronic Resource
    Electronic Resource
    Book reviews (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 313-326 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464434
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  • 4
    Electronic Resource
    Electronic Resource
    Editorial: Software survey section (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. I 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464436
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  • 5
    Electronic Resource
    Electronic Resource
    Resource management and behavioural ecology: A Conference in Celebration of the 60th Birthday of Colin Clark 24–26 July 1991 University of British Columbia, Cancouver, B.C. (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 327-327 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02464435
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  • 6
    Electronic Resource
    Electronic Resource
    The statistical correlation of nucleotides in protein-coding DNA sequences (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 345-353 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The statistical correlation of nucleotides in a DNA sequence is described by a set of redundanciesD 1,D 2,D 3,... By calculation of {D n} of 2341 coding regions of nucleic acid sequences it is demonstrated that about 2/3 of sequences has correlation length ≤2, 10% of sequences—correlation with 3-periodicity and others—long range aperiodic correlations. The implications of the results from the interactions of random mutation and natural selection are discussed briefly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460722
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  • 7
    Electronic Resource
    Electronic Resource
    Autocatalytic membrane conductance and memory (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 327-343 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A basic characteristic of biological memory is that it has a graded duration, which, even for socalled short-term memory, can vary from minutes to days (i.e. over about three orders of magnitude), depending on the training protocol, which one can think of as determining the “strength” of the memory. Furthermore, the molecular analysis of simple learning in invertebrates has revealed many examples where “learning” is produced by adecrease in an appropriate membrane conductance. This paper provides a quantitative analysis of a simple kinetic scheme where by a conductance decrease can be produced by repetitive nerve impulses, with a duration that varies with stimulus frequency. The simplest model considered is based on the actual kinetics of the naturally-occurring ionophore Monazomycin. This model yields durations ranging only over a factor of about 10, for reasonable parameter values. However, a simple modification of the model yields memory durations ranging over three or more orders of magnitude. We also show that Monazomycin-like kinetics can appear as the result of a combination of simple uni- and bi-molecular reactions, thus making more plausible the possibility that the effects described here may operate in actual biological systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02460721
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  • 8
    Electronic Resource
    Electronic Resource
    Statistical evaluation of dendritic growth models (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 579-589 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A mathematical model (Kliemann, W. 1987.Bull. math. Biol. 49, 135–152.) that predicts the quantitative branching pattern of dendritic tree was evaluated using the apical and basal dendrites of rat hippocampal neurons. The Wald statistics for χ2-test was developed for the branching pattern of dendritic trees and for the distribution of the maximal order of the tree. Using this statistic, we obtained a reasonable, but not excellent, fit of the mathematical model for the dendritic data. The model's predictability of branching patterns was greatly enhanced by replacing one of the assumptions used for the original model “splitting of branches for all dendritic orders is stochastically independent”, with a new assumption “branches are more likely to split in areas where there is already a high density of branches”. The modified model delivered an excellent fit for basal dendrites and for the apical dendrites of hippocampal neurons from young rats (30–34 days postpartum). This indicates that for these cells the development of dendritic patterns is the result of a purely random and a systematic component, where the latter one depends on the density of dendritic branches in the brain area considered. For apical dendrites there is a trend towards decreasing pattern predictability with increasing age. This appears to reflect the late arrival of afferents and subsequent synaptogenesis proximal on the apical dendritic tree of hippocampal neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458630
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  • 9
    Electronic Resource
    Electronic Resource
    Computer simulations of cell-target encounter including biased cell motion toward targets: Single and multiple cell-target simulations in two dimensions (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 591-621 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In order for immune cells to carry out many of their functions, including clearance of infectious agents from tissue, they must first encounter their targets in the tissue. This encounter process is often the rate-limiting step in the overall function. Most immune cells exhibit chemotactic ability, and previous continuum models for encounter rates and dynamics have shown that chemotaxis can be a great advantage to cells by greatly increasing encounter rates relative to those for randomly moving cells. This paper describes computer simulations of discrete cell-target encounter events in two dimensions, for the two cases considered by the continuum models: where only a single cell and a single target are present, and where many cells and targets are present. The results of these simulations verify our previous model predictions that a small amount of chemotactic bias dramatically decreases the encounter time, while further increases in the amount of bias have a much smaller effect. Chemotactic ability is shown to be an important determinant of the kinetics of target clearance, and its effects depend on the initial cell-target ratio and the initial distributions of cells and targets. To the best of our knowledge, this work provides the first computer simulations of particle-target encounter in which there is biased motion of particles toward their targets, and is therefore of general interest beyond specific application to immune cell function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458631
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  • 10
    Electronic Resource
    Electronic Resource
    Book reviews (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 657-663 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458634
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  • 11
    Electronic Resource
    Electronic Resource
    One-way blocks in cardiac tissue: A mechanism for propagation failure in purkinje fibres (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 881-899 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The concept of a one-way block, arising from a region of depressed tissue, has remained central to theories for cardiac arrhythmias. We show that both the geometry of a depressed region and spatial heterogeneities in depression are key factors for inducing such a block. By using an asymptotic approximation, known as the eikonal equation, to model qualitatively the movement of a depolarization wave-front down a Purkinje fibre bundle, we show how a one-way block in conduction may result from asymmetric constriction in the width of a depressed bundle. We demonstrate that this theory is valid for biologically relevant parameters and simulate a one-way block by numerically solving the eikonal approximation. We consider the case of non-uniform depression, where the planar travelling wave speed is spatially dependent. Here, numerical simulations indicate that such a spatial dependency may, in itself, be sufficient to produce a one-way block.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461489
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  • 12
    Electronic Resource
    Electronic Resource
    A system dynamics model of island biogeography (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 911-940 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The MacArthur-Wilson equilibrium theory of island biogeography has been one of the more influential concepts in modern biogeography and ecology. In this paper, we synthesize the theory and examine effects of different immigration/extinction rate-species diversity curves on original predictions from the theory by using the System Dynamics simulation modeling approach. Moreover, we develop a comprehensive and generic System Dynamics model to incorporate a variety of recent modifications and extensions of the theory, including area effect, distance effect, competition effect, habitat diversity effect, target effect, and rescue effect. Through computer simulation with STELLA, a more profound understanding of the theory of island biogeography can be gained. The System Dynamics modeling approach is especially appropriate for such a study because it maximizes the utilization of the ecological data by incorporating qualitative information so that a complex, imprecisely-defined ecological system can be studied quantitatively, effectively, and comprehensively. Our simulation results show that different monotonic rate-species diversity curves do not affect the essence of the theory of island biogeography, while the magnitude of equilibrium species diversity may be greatly affected. Non-monotonic rate-species diversity curves may result in potential multiple equilibria of species diversity. In addition, our model suggests that a non-monotonic relationship may exist between the equilibrium turnover rate and island area and between the equilibrium turnover rate and distance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461491
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  • 13
    Electronic Resource
    Electronic Resource
    The estimation of the Kolmogorov entropy from a time series and its limitations when performed on EEG (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 665-678 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A method to estimate a lower bound of the Kolmogorov entropy—the so calledK 2-entropy—from a time series is presented which avoids use of the generalized correlation integral. The influence of the norm is studied. The method is demonstrated on some standard examples. The entropy of the attractor apparent in the EEG of the foetal sheep is estimated and the results are compared with results obtained from synthesized data featuring some basic properties of EEG. This gives an insight into the limitations of the procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461547
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  • 14
    Electronic Resource
    Electronic Resource
    Analysis of oscillations in yeast continuous cultures by a new simplified model (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 685-700 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The autonomous oscillations in yeast continuous cultures are investigated analytically and related to the behaviour of the single cell by means of a suitable modified version of Monod’s classical chemostat model. Two main cell phases or states are considered to account for the experimentally observed changes occurring in the cell growth course: the budded phase and the unbudded one. Thus, a sort of two compartment structure is given to the total biomass. The model so far obtained allows one to analyse the local properties of the predicted steady states under various assumptions, both on the yield coefficients and the specific growth rates. Necessary conditions for the local instability are derived and the existence of stable limit cycles is shown by computer simulation. With respect to the qualitative changes in the metabolic parameters, this analysis agrees with the results obtained by simulation of complex structured and segregated models. However, the oscillation period is too long compared with the experimental one and this fact may be mainly due to the strong simplifying assumptions on the dynamic evolution of the transfer rates between the two compartments. The model’s usefulness seems until now restricted to the identification of the relationships between the cell cycle regulation and the oscillation triggering.
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    URL: http://dx.doi.org/10.1007/BF02461549
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  • 15
    Electronic Resource
    Electronic Resource
    Analysis of chemotactic bacterial distributions in population migration assays using a mathematical model applicable to steep or shallow attractant gradients (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 721-749 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The mathematical model developed by Riveroet al. (1989,Chem. Engng Sci. 44, 2881–2897) is applied to literature data measuring chemotactic bacterial population distributions in response to steep as well as shallow attractant gradients. This model is based on a fundamental picture of the sensing and response mechanisms of individual bacterial cells, and thus relates individual cell properties such as swimming speed and tumbling frequency to population parameters such as the random motility coefficient and the chemotactic sensitivity coefficient. Numerical solution of the model equations generates predicted bacterial density and attractant concentration profiles for any given experimental assay. We have previously validated the mathematical model from experimental work involving a step-change in the attractant gradient (Fordet al., 1991Biotechnol. Bioengng.37, 647–660; For and Lauffenburger, 1991,Biotechnol. Bioengng,37, 661–672). Within the context of this experimental assay, effects of attractant diffusion and consumption, random motility, and chemotactic sensitivity on the shape of the profiles are explored to enhance our understanding of this complex phenomenon. We have applied this model to various other types of gradients with successful intepretation of data reported by Dalquistet al. (1972,Nature New Biol. 236, 120–123) forSalmonella typhimurum validating the mathematical model and supportin the involvement of high and low affinity receptors for serine chemotaxis by these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461551
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  • 16
    Electronic Resource
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    Book reviews (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 797-804 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461554
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  • 17
    Electronic Resource
    Electronic Resource
    Rook’s tour representation of the genetic code (1991)
    Springer
    Bulletin of mathematical biology 53 (1991), S. 845-851 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Disconnected recurrences of the stop signal, serine and arginine appear in the original representation of the genetic code, and of the stop signal, arginine, serine and leucine in the codon ring representation. To achieve connectedness along with structural continuity, arook’s tour representation is presented here. On the basis of structural similarities and disparities in their side groups, each of the 20 amino acids is associated with a domain comprised of from one to six contiguous squares on the chess board. As the rook moves on the chess board, it reaches all 64 squares in the ordering of the codon numbers, which prescribe the codons by a simple formula based on the position and size of the nucleotides in a triplet. Recurrences of the stop signal, arginine and serine occur naturally on the tour as the rook enters each of the latter domains for the second time. A mathematical equivalent of the rook’s tour may enter as a programming device in the implementation of the code by the RNAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02461487
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  • 18
    Electronic Resource
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    Book review (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 195-196 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1997.0018
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  • 19
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    A mathematical model for fibroblast and collagen orientation (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 101-129 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Due to the increasing importance of the extracellular matrix in many biological problems, in this paper we develop a model for fibroblast and collagen orientation with the ultimate objective of understanding how fibroblasts form and remodel the extracellular matrix, in particular its collagen component. The model uses integrodifferential equations to describe the interaction between the cells and fibers at a point in space with various orientations. The equations are studied both analytically and numerically to discover different types of solutions and their behavior. In particular we examine solutions where all the fibroblasts and collagen have discrete orientations, a localized continuum of orientations and a continuous distribution of orientations with several maxima. The effect of altering the parameters in the system is explored, including the angular diffusion coefficient for the fibroblasts, as well as the strength and range of the interaction between fibroblasts and collagen. We find the initial conditions and the range of influence between the collagen and the fibroblasts are the two factors which determine the behavior of the solutions. The implications of this for wound healing and cancer are discussed including the conclusion that the major factor in determining the degree of scarring is the initial deposition of collagen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1997.0027
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  • 20
    Electronic Resource
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    Extinction times and phase transitions for spatially structured closed epidemics (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 215-230 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract This paper considers the time to extinction for a stochastic epidemic model of SEIR form without replacement of susceptibles. It first shows how previous rigorous results can be heuristically explained in terms of the more transparent dynamics of an approximating deterministic system. The model is then extended to include a host population structured into patches, with weak nearest-neighbour mixing of infection. It is shown, by considering the approximating deterministic system, that the expected time to extinction in a population of n + 1 patches each of size N is of the form a log N + bn, provided that N 〉 N c where N c is a critical patch size below which transits are unlikely to occur. This corresponds to the simple decomposition of the time of an epidemic into the time it takes to spread through one patch plus the time it takes to transit to each of n successive patches. Expressions for this threshold and the coefficients of the time to extinction are given in terms of the transmission parameters of infection and the coupling strength between patches. These expressions are compared with numerical results using parameters relevant to a study of phocine distemper virus in North Sea seals, and the agreement is found to be good for large and small N. In the region when N ≈ N c , where transits may or may not occur, interesting transitional behaviour is seen, leading to a non-monotonicity of the extinction time as a function of N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1997.0014
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  • 21
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    Book reviews (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 409-415 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1997.0019
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  • 22
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    The loss of immunity in directly transmitted infections modeling: Effects on the epidemiological parameters (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 355-372 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract When directly transmitted infectious diseases are modeled assuming an everlasting induced immunity (and constant contact rate), there are well-established formulas to deal with, which is not true if we include the loss of induced immunity. In general, the immunity induced by the disease is everlasting. We propose a model considering the loss of immunity and present methods for the estimation of two epidemiological parameters: the force of infection and the basic reproduction ratio. We also analyze the effects of the loss of immunity on these parameters. Based on these results, we conclude that reinfection can play an important role in highly vaccinated populations.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0031
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  • 23
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    Models for the length distributions of actin filaments: I. Simple polymerization and fragmentation (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 449-475 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We studied mathematical models for the length distributions of actin filaments under the effects of polymerization/depolymerization, and fragmentation. In this paper, we emphasize the effects of these two processes acting alone. In this case, simple discrete and continuous models can be derived and solved explicitly (in several special cases), making the problem interesting from a modeling and pedagogical point of view. In a companion paper (Ermentrout and Edelstein-Keshet, 1998, Bull. Math. Biol. 60, 477–503) we investigate what happens when the processes act together, with particular attention to fragmentation by gelsolin, and with a greater level of biological detail.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0011
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  • 24
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    Parallel dose-response curves in combination experiments (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 197-213 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A possible experimental design for combination experiments is to compare the doseresponse curve of a single agent with the corresponding curve of the same agent using either a fixed amount of a second one or a fixed dose ratio. No interaction is then often defined by a parallel shift of these curves. We have performed a systematic study for various types of doseresponse relations both for the dose-additivity (Loewe additivity) and for the independence (Bliss independence) criteria for defining zero interaction. Parallelism between doseresponse curves of a single agent and those of the same agent in the presence of a fixed amount of another one is found for the Loewe-additivity criterion for linear doseresponse relations. For nonlinear relations, one has to differentiate between effect parallelism (parallel shift on the effect scale) and dose parallelism (parallel shift on the dose scale). In the case of Loewe additivity, zero-interaction dose parallelism is found for power, Weibull, median-effect and logistic doseresponse relations, given that special parameter relationships are fulfilled. The mechanistic model of competitive interaction exhibits dose parallelism but not effect parallelism for Loewe additivity. Bliss independence and Loewe additivity lead to identical results for exponential doseresponse curves. This is the only case for which dose parallelism was found for Bliss independence. Parallelism between single-agent doseresponse relations and Loewe additivity mixture relations is found for examples with a fixed doseratio design. However, this is again not a general property of the design adopted but holds only if special conditions are fulfilled. The comparison of combination doseresponse curves with single-agent relations has to be performed taking into account both potency and shape parameters. The results of this analysis lead to the conclusion that parallelism between zero interaction combination and single-agent doseresponse relations is found only for special cases and cannot be used as a general criterion for defining zero-interaction in combined-action assessment even if the correct potency shift is taken into account.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0009
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  • 25
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    Pattern formation in a generalized chemotactic model (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 1-26 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Many models have been proposed for spatial pattern formation in embryology and analyzed for the standard case of zero-flux boundary conditions. However, relatively little attention has been paid to the role of boundary conditions on the form of the final pattern. Here we investigate, numerically, the effect of nonstandard boundary conditions on a model pattern generator, which we choose to be of a cell-chemotactic type. We specifically focus on the role of boundary conditions and the effects of scale and aspect ratio, and study the spatiotemporal dynamics of pattern formation. We illustrate the properties of the model by application to the spatiotemporal sequence of skeletal development.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0010
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  • 26
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    A continuum mechanics approach to determining the cellular velocity field within a wool follicle (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 79-100 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A model, based on the principles of continuum mechanics, is presented for the analysis of cell-velocity fields within wool follicles. The model requires specification of three follicle characteristics in the form of spatially varying fields: viscosity, cell density and cell production rate. The viscosity is introduced as an attempt to model both complex intercellular interactions and individual cell deformation as the cells move. It is demonstrated that the distribution of cell production is more important than axial variation in viscosity in determining the overall flow pattern.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0025
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  • 27
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    Modelling the metabolic versatility of a microbial trichome (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 131-150 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A microbial trichome extracts nutrients from its immediate surroundings. It may also oxidize electron donors, reduce electron acceptors, and exude the ‘waste’ products of endogenous redox metabolism. Finally, it may effect light harvesting. These exchange fluxes are summed up in a generic model, which covers photoautotrophs as well as chemoheterotrophs. The focus is on endogenous metabolism and the cellular homeostasis of both reducing and phosphorylating equivalents. A novel result is the formulation of four ‘rules’, akin to the Pasteur effect, which govern the compatibility of endogenous metabolism with various assimilatory processes.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0026
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    Optimal harvesting for a predator-prey metapopulation (1998)
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    Bulletin of mathematical biology 60 (1998), S. 49-65 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract In this paper we present a deterministic, discrete-time model for a two-patch predator-prey metapopulation. We study optimal harvesting for the metapopulation using dynamic programming. Some rules are established as generalizations of rules for a single-species metapopulation harvesting theory. We also establish rules to harvest relatively more (or less) vulnerable prey subpopulations and more (or less) efficient predator subpopulations.
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    URL: http://dx.doi.org/10.1006/bulm.1997.0005
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    Wavelet-based analysis of human blood-flow dynamics (1998)
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    Bulletin of mathematical biology 60 (1998), S. 919-935 
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    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract To analyze signals measured from human blood flow in the time-frequency domain, we used the wavelet transform which gives good time resolution for high-frequency components and good frequency resolution for low-frequency components. Five characteristic frequency peaks, corresponding to five almost periodic rhythmic activities, were found on the time scale of minutes. These oscillations were characterized by time and spatial invariant measures. The potential of this approach in studying the blood-flow dynamics was illustrated by revealing differences between the groups of control subjects and athletes.
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    Book review (1998)
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    Bulletin of mathematical biology 60 (1998), S. 997-998 
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    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1998.0065
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    Diffusively coupled bursters: Effects of cell heterogeneity (1998)
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    Bulletin of mathematical biology 60 (1998), S. 1167-1200 
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    Notes: Abstract The interaction of a pair of weakly coupled biological bursters is examined. Bursting refers to oscillations in which an observable slowly alternates between phases of relative quiescence and rapid oscillatory behavior. The motivation for this work is to understand the role of electrical coupling in promoting the synchronization of bursting electrical activity (BEA) observed in the β-cells of the islet of Langerhans, which secrete insulin in response to glucose. By studying the coupled fast subsystem of a model of BEA, we focus on the interaction that occurs during the rapid oscillatory phase. Coupling is weak, diffusive and non-scalar. In addition, non-identical oscillators are permitted. Using perturbation methods with the assumption that the uncoupled oscillators are near a Hopf bifurcation, a reduced system of equations is obtained. A detailed bifurcation study of this reduced system reveals a variety of patterns but suggests that asymmetrically phase-locked solutions are the most typical. Finally, the results are applied to the unreduced full bursting system and used to predict the burst pattern for a pair of cells with a given coupling strength and degree of heterogeneity.
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    Modeling actin filament reorganization in endothelial cells subjected to cyclic stretch (1998)
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    Bulletin of mathematical biology 60 (1998), S. 1017-1037 
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    ISSN: 1522-9602
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    Notes: Abstract Hemodynamic forces affect endothelial cell morphology and function. In particular, circumferential cyclic stretch of blood vessels, due to pressure changes during the cardiac cycle, is known to affect the endothelial cell shape, mediating the alignment of the cells in the direction perpendicular to stretch. This change in cell shape proceeds a drastic reorganization at the internal level. The cellular scaffolding, mainly composed of actin filaments, reorganize in the direction which later becomes the cell’s long axis. How this external mechanical stimulus is ’sensed’ and transduced into the cell is still unknown. Here, we develop a mathematical model depicting the dynamics of actin filaments, and the influence of the cyclic stretch of the substratum based on the experimental evidence that external stimuli may be transduced inside the cell via transmembrane proteins which are coupled with actin filaments on the cytoplasmic side. Based on this view, we investigate two approaches describing the formulation of the transduction mechanisms involving the coupling between filaments and the membrane proteins. As a result, we find that the mechanical stimulus could cause the experimentally observed reorganization of the entire cytoskeleton simply by altering the dynamics of the filaments connected with the integral membrane proteins, as described in our model. Comparison of our results with previous studies of cytoskeletal dynamics reveals that the cytoskeleton, which, in the absence of the effect of stretch would maintain its isotropic distribution, slowly aligns with the precise direction set by the external stimulus. It is found that even a feeble stimulus, coupled with a strong internal dynamics, is sufficient to align actin filaments perpendicular to the direction of stretch.
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    Emergence of donor control in patchy predator—prey systems (1998)
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    Bulletin of mathematical biology 60 (1998), S. 1149-1166 
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    ISSN: 1522-9602
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    Notes: Abstract We study a general predator—prey system in a spatially heterogeneous environment. The predation process, which occurs on a behavioural time-scale, is much faster than the other processes (reproduction, natural mortality and migrations) occurring on the population dynamics time-scale. We show that, taking account of this difference in time-scales, and assuming that the prey have a refuge, the dynamics of the system on a slow time-scale become donor-controlled. Even though predators may control the prey density locally and on a behavioural fast time-scale, nevertheless, both globally and on a slow time-scale, the prey dynamics are independent of predator density: the presence of predators generates a constant prey mortality. In other words, in heterogeneous environments, the prey population dynamics depend in a switch-like manner on the presence or absence of predators, not on their actual density.
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    Mean oscillation of functions and the Paley-Wiener space (1998)
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    The journal of Fourier analysis and applications 4 (1998), S. 283-297 
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    ISSN: 1531-5851
    Keywords: Primary 42B25 ; 30D10 ; Secondary 26A16 ; 46B45 ; 47B10 ; 47B35 ; Mean oscillation ; Paley-Wiener space ; Besov spaces ; wavelets ; commutators ; Hankel operators ; Schatten-von Neumann ideals
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    Notes: Abstract The oscillatory behavior of functions with compactly supported Fourier transform is characterized in a quantified way using various function spaces. In particular, the results in this article show that the oscillations of a function at large scale are comparable to the oscillations of its samples on an appropriate discrete set of points. Several open questions about spaces of sequences are answered and applications in the study of commutator operators on the Paley-Wiener space are shown.
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    Wavelets on fractals and besov spaces (1998)
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    The journal of Fourier analysis and applications 4 (1998), S. 329-340 
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    Keywords: 42C15 ; 46E35 ; Wavelets ; function spaces ; fractals
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    Notes: Abstract Wavelets on self-similar fractals are introduced. It is shown that for certain totally disconnected fractals, function spaces may be characterized by means of the magnitude of the wavelet coefficients of the functions.
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    Gibbs' phenomenon for sampling series and what to do about it (1998)
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    The journal of Fourier analysis and applications 4 (1998), S. 357-375 
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    ISSN: 1531-5851
    Keywords: 42C15 ; 94A12 ; wavelets ; interpolation ; orthogonal expansions
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    Notes: Abstract Gibbs' phenomenon occurs for most orthogonal wavelet expansions. It is also shown to occur with many wavelet interpolating series, and a characterization is given. By introducing modifications in such a series, it can be avoided. However, some series that exhibit Gibbs' phenomenon for orthogonal series do not for the associated sampling series.
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    Some results on sensitivity of general input-output systems (1991)
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    Circuits, systems and signal processing 10 (1991), S. 71-89 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We consider general input-output systems, which need not be of a feedback type, that are governed by nonlinear operator equations which relate the input, state, and output. Assuming that these equations depend on a parameterA which is allowed to vary in a neighborhood of a “nominal value”A 0 , we study the dependence of the output onA when the input is fixed. Essentially, we call a system insensitive if the output depends continuously onA. Two insensitivity concepts are introduced, and it is shown that certain monotonicity-like conditions ensure insensitivity. Also, several particular cases of the governing equations are studied. As examples, a control system described by a singular system of ordinary differential equations and a nonlinear feedback system are discussed.
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    On limit cycles inn-order direct-form digital filters (1991)
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    Circuits, systems and signal processing 10 (1991), S. 153-161 
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    Notes: Abstract The relationship between the elements in the vector of any limit cycle due to rounding in ann-order direct-form digital filter is established. Some bounds on the elements in such vectors are also determined. Sufficient conditions for the accessibility of period-r limit cycles due to rounding inn-order digital filters are presented.
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    Direction-of-arrival estimation in applications with multipath and few snapshots (1991)
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    Circuits, systems and signal processing 10 (1991), S. 327-342 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper analyzes two direction-of-arrival (DOA) estimation algorithms used in the presence of multipath propagation and with very few snapshots. The conditional maximum likelihood (CML) algorithm and the method of direction estimation (MODE) are discussed. The estimates provided by these algorithms are shown to coincide for large number of snapshots or large signal-to-noise ratio. Necessary and sufficient conditions are derived for the algorithms to yield unique estimates. It is shown that their uniqueness conditions coincide with the minimal uniqueness condition on the array, that is independent of the algorithm used (if the array does not satisfy this minimal condition, no DOA estimation method can give unique estimates). Numerical examples are presented to demonstrate the theoretical results.
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    Robust stability and senstivity of input-output systems over extended spaces (1991)
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    Circuits, systems and signal processing 10 (1991), S. 361-389 
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    Notes: Abstract In Part I of this paper we consider a general model of an input-output system governed by nonlinear operator equations that relate the system's input, state, and output, all of which are elements in extended spaces. This model encompasses feedback systems as a special case. Assuming that the equations governing the system depend on a parameterA that is allowed to vary in a neighborhoodN r (A 0) of a nominal valueA 0 in a linear space, we study conditions under which the system is stable for everyA ε Nr(A0), i.e., when the system exhibits robust stability. By stability we essentially mean that the input-output operator is continuous. Depending on the type of continuity of a map between two extended spaces, four concepts of robustness are introduced. The main results, Theorems 1 and 2, furnish sufficient conditions for a system to be robust in the respective sense. Basically, they show that if the nominal system satisfies a certain condition guaranteeing its stability, and the operators appearing in the governing equations depend continuously on the parameterA, then we have robust stability. As examples illustrating the applications of our results we discuss (1) a feedback-feedforward system, in particular the case when the extended space consists of locally square-integrable functions or functions continuous on [0, ∞), and (2) a time-varying dynamical system described by a linear vector differential equation, whose variables are continuous functions on [0, ∞) which decrease exponentially to zero ast → ∞. At the end of the paper some modifications of the presented theory are discussed.
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    Higher-order statistics-based input/output system identification and application to noise cancellation (1991)
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    Circuits, systems and signal processing 10 (1991), S. 485-511 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Higher-than-second-order statistics-based input/output identification algorithms are proposed for linear and nonlinear system identification. The higher-than-second-order cumulant-based linear identification algorithm is shown to be insensitive to contamination of the input data by a general class of noise including additive Gaussian noise of unknown covariance, unlike its second-order counterpart. The nonlinear identification is at least as optimal as any linear identification scheme. Recursive-least-squares-type algorithms are derived for linear/nonlinear adaptive identification. As applications, the problems of adaptive noise cancellation and time-delay estimation are discussed and simulated. Consistency of the adaptive estimator is shown. Simulations are performed and compared with the second-order design.
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    URL: http://dx.doi.org/10.1007/BF01194885
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    A space-time-filtered Viterbi receiver for CCI/ISI reduction in TDMA systems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 85-102 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we present a hybrid space-time-filtered Viterbi receiver using multiple antennas for co-channel interference (CCI) reduction and intersymbol interference (ISI) equalization in a slow Rayleigh fading channel. In this approach, a space-time filter is first applied at the antenna outputs to maximize the signal-to-interference-plus-noise ratio (SINR), and the scalar output is then sent to a Viterbi equalizer. We propose a closed-form solution to jointly determine the weight vector for the space-time filter and the channel vector for the Viterbi equalizer. We also examine the need for a whitening filter prior to the Viterbi equalizer and show that it only marginally improves the performance. Simulation results are provided to validate our approach and to compare the performance of our receiver with that of different existing receivers.
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    Sydney Richard Parker 1923–1996 (1998)
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    Circuits, systems and signal processing 17 (1998), S. i 
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    Parametric signal processing of anechoic data from prosthetic heart valve testing (1998)
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    Circuits, systems and signal processing 17 (1998), S. 123-136 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Prosthetic heart valves have been responsible for extending the life spans and improving the quality of life of many people with serious heart conditions. Even though the heart valves are extremely reliable, eventually they are susceptible to the long-term fatigue and structural failure effects expected for mechanical devices operating over long periods of time. In [2] a classification procedure was developed using spectral features obtained from acoustic signals to determine the condition of the prosthetic heart valve. Although this classification procedure has produced very encouraging results, this method still lacks a fundamental physical description of the sounds produced by the valve during normal operation. In order to obtain a better understanding of the valve acoustic response, we have performed a set of anechoic tests. In this paper, we describe the anechoic experiment and also present limited transient response results. This transient information will eventually be used to identify and improve the features used to classify the valve condition.
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    On neural network design — Part I: Using the MVQ algorithm (1998)
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    Circuits, systems and signal processing 17 (1998), S. 195-218 
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    Notes: Abstract In this two-part study we present a new design methodology for neural classifiers. The design procedure utilizes a multiclass vector quantization (MVQ) algorithm for information extraction from the training set. The extracted information suffices to specify the hidden layer in a canonical neural network architecture. The extracted information also leads to the specification of neuron inhibition rules and subsequently the design of the hidden layer-to-output map. In Part I of the study we focus attention on the MVQ algorithm and how it is used to extract information from a training set. The extracted information is referred to as thecodebook. The codebook is used to directly specify the hidden layer. This specification can take the form of a perceptron layer, a radial basis layer, or a heterogeneous layer involving a mixture of neuron types. These and otherh-layer specifications are determined directly from the same extracted information. The MVQ codebook also suffices to scale the activation function of each neuron. In Part II we consider the nonsimplistic hidden layer-to-output map design. We note that the MVQ algorithm, as it extracts information, decomposes the design set into disjoint neighborhoods. For each neighborhood we identify subsets of the hidden layer neurons, which are significant sensors for the neighborhood. For each such subset we construct an output map. Inhibition rules are established to ensure that the proper output map is activated. In benchmark simulations the overall design exhibits excellent performance, to the extent that we are hard pressed to identify bounds on performance, if any.
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    A holographic transform domain image watermarking method (1998)
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    Circuits, systems and signal processing 17 (1998), S. 361-389 
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    Notes: Abstract A transform domain image tagging orwatermarking method that survives image cropping (and, hence, is “holographic”) was proposed at Bell Labs in September 1994. This report analyzed in detail the various properties of this method and introduces an optimal procedure for watermark recovery.
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    A sectoring algorithm for exact computation of the frequency response of linear interval systems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 483-493 
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    Notes: Abstract An algorithm for the exact computation of the frequency responses of linear interval systems is obtained. For the computation a sectoring stage is added to an elimination algorithm to eliminate interior curves. It is shown that the intersection of a ray and the frequency response set is an empty set or a line segment whose endpoints are extrema of the functions defined. Required mathematical analysis tools for the development of the sectoring algorithm and an illustrative example are provided.
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    The fundamental subspace sequences of matrix pencils: A toeplitz matrix unified characterization (1998)
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    Circuits, systems and signal processing 17 (1998), S. 559-574 
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    Notes: Abstract The geometric theory of the domain of an ordered pair (F, G) of matrices or the geometry associated with matrix pencils provides a unifying framework for the study of algebraic, dynamic and feedback properties of linear singular systems. The key concepts and tools of the geometry are the notions of the (F, G)-, (G, F)-invariance and a set of subspace sequences. In this paper, an alternative characterization of these sequences is given based on the properties of the partitioned null spaces of appropriate sequences of Toeplitz matrices defined by the (F, G) pair. The results provide a simple procedure for the computation of the limit spaces of these sequences and clearly cover corresponding problems of the singular, implicit systems theory.
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    Active noise compression systems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 667-682 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a new concept of narrowband and broadband active noise compression (ANCom) systems which improves the conventional active noise equalization (ANE) technique to meet some practical requirements. By using a variable equalization coefficient, the narrowband ANCom system can automatically switch among the four different operating modes of narrowband ANE, according to the primary noise power. As a result, it can “compress” the narrowband noise into a desired power range when the primary noise power varies drastically. Compared to a conventional broadband ANE system, the novel broadband ANCom system not only has the ability to shape the residual noise power spectrum, but can also compress the residual noise power into a predetermined dynamic range as the narrowband AN-Com does. Theoretical analyses are conducted for both the narrowband ANCom and broadband ANCom systems. Simulation results show that the proposed algorithms work well in both static and dynamic situations.
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    A note on representation theorems for linear discrete-space systems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 703-708 
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    Notes: Abstract The cornerstone of the theory of discrete-space single-input single-output linear systems is the idea that every such system has an input-output mapH that can be represented by a convolution or the familiar generalization of a convolution. This thinking involves an oversight, which, for the case of bounded inputs mapped continuously into bounded outputs, was recently corrected by adding an additional term to the representation. Here we give a more general result that addresses an important larger family of inputs.
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    Robust stabilization of singular systems withH ∞-bounded uncertainty (1998)
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    Circuits, systems and signal processing 17 (1998), S. 737-755 
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    Notes: Abstract In this paper the problem of robust stabilizing a linear, time-invariant singular system is studied. The characterization is given in terms ofH ∞-bounded perturbations to the numerator and denominator factors of its normalized left coprime factorization. An optimal stability margin is provided in terms of the definition of the Hankel norm of a singular system. The Hankel norm is computed using two generalized Lyapunov equations.
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    Design of sharp linear-phase FIR bandstop filters using the frequency-response-masking technique (1998)
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    Circuits, systems and signal processing 17 (1998), S. 1-27 
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    Notes: Abstract A novel computationally efficient realization of sharp linear-phase finite impulse response (FIR) bandstop filters is proposed. The synthesis scheme for the bandstop filters is derived from variations of the frequency-response-masking technique. Five realization structures are presented in this paper for the synthesis of five different classes of bandstop filters. Approximate expressions for the optimal value of the impulse response up-sampling ratio (M) and the corresponding number of multipliers are derived.
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    Capon estimation of covariance sequences (1998)
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    Circuits, systems and signal processing 17 (1998), S. 29-49 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Estimating the covariance sequence of a wide-sense stationary process is of fundamental importance in digital signal processing (DSP). A new method, which makes use of Fourier inversion of the Capon spectral estimates and is referred to as theCapon method, is presented in this paper. It is shown that the Capon power spectral density (PSD) estimator yields an equivalent autoregressive (AR) or autoregressive moving-average (ARMA) process; hence, theexact covariance sequence corresponsing to the Capon spectrum can be computed in a rather convenient way. Also, without much accuracy loss, the computation can be significantly reduced via an approximate Capon method that utilizes the fast Fourier transform (FFT). Using a variety of ARMA signals, we show that Capon covariance estimates are generally better than standard sample covariance estimates and can be used to improve performances in DSP applications that are critically dependent on the accuracy of the covariance sequence estimates.
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    Signal processing based on parameter structural modeling and separation of highly correlated signals of known structure (1998)
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    Circuits, systems and signal processing 17 (1998), S. 51-68 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Results in the study of signal processing based on the use of parameter structural modeling (PSM) are presented. First, we introduce a special form of time-series modeling based on signal-dependent building blocks. Such modeling is used in the design of a nestedform transversal structure, known as a composite filter, based on a shift-invariant finite impulse resonse (FIR) as well as infinite impulse response (IIR) building blocks. The newly proposed composite PSM model (CPSM) possesses a unique feature, namely, its ability to suppress one signal of a given structure, while at the same time being ideally transparent to another one. The intrinsic property of this proposed CPSM is its enhanced insensitivity with respect to noise as well as its ability to fast track, in contrast to the commonly used linear line-enhancer based on conventional autoregressive moving average (ARMA), thus leading to a more practically sound processing of short-duration signals. It is shown that the proposed time-series modeling based on CPSM can be effectively applied towards the separation of superimposed signals of heavily overlapping spectra. Next, the parameter-invariant nonlinear structural signal representation based on shift-invariant CPSM is presented. The use of this model in the design of annihilation operators (AO) is described, and composite parameter-free structural modeling (CPFSM) is developed. Based on this model, two canonical forms of the parameter-invariant null filters (PINF) are presented, and their use in the suppression of a given class of signals, independently of the values of theira priori unknown parameters, is illustrated. The paper also presents some simulation examples illustrating the application of the proposed CPSM and CPFSM in solving problems of detection and parameter estimation in the presence of highly non-Gaussian, mainly signal-like interferences.
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    URL: http://dx.doi.org/10.1007/BF01213969
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    Nonlinear digital filters mimicking cellular neural networks (1998)
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    Circuits, systems and signal processing 17 (1998), S. 69-83 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This work is motivated by the need forFaithful digital simulation of cellular neural networks (CNNs) that maintains most of their qualitative properties of stability and convergence. An interconnection of nonlinear digital filters mimicking behaviors of the analog CNNs is proposed, and the main properties are studied in detail. The discrete model obtained is proven to have the same convergence properties as the original analog network. The key to this development is the use of anAppropriate discretization scheme. Our discrete approximation to the nonlinear state-space representation of cellular neural networks is such that the Lyapunov function used to show convergence in analog cellular neural networks is still a Lyapunov function (when appropriately discretized) for our nonlinear digital filter network. This is in contrast to other digital simulations of CNNs, which have not been proven to preserve the convergence properties. The network of nonlinear digital filters so introduced thus adds another item to the catalog of digital filters obtained viaappropriate discretization of analog circuits, e.g., wave digital filters, orthogonal filters, and certain other of their more recently studied nonlinear counterparts.
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    URL: http://dx.doi.org/10.1007/BF01213970
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    Direct multiple-channel blind equalization (1998)
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    Circuits, systems and signal processing 17 (1998), S. 117-122 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, the problem of blind channel identification and equalization is reviewed, and some recent results are presented.
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    URL: http://dx.doi.org/10.1007/BF01213973
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    Halfband filters and Hilbert transformers (1998)
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    Circuits, systems and signal processing 17 (1998), S. 137-164 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents in summarizing form a description of halfband filters and the related symmetrical Hilbert transformers. It starts with the two complemetary relations by which halfband filters are defined and the consequences for their impulse responses. The idealized versions of the frequency responses of halfband lowpasses and Hilbert transformers are introduced, and the related tolerance schemes that realized systems must satisfy are described. Using their frequency responses, the transformation of one filter type into the other is presented in general form. The design of finite impulse response (FIR)-halfband filters and their relation to corresponding Hilbert transformers are recalled, using maximally flat and Chebyshev approximations as examples. It is shown that the relation between both types of systems can be used for the infinite impulse response (IIR) case as well. The design of IIR-halfband filters is presented for systems with approximately linear phase and for those with minimum phase again for maximally flat and Chebyshev approximations. The design methods are partly new. The general procedure for the transformation into Hilbert transformers yields noncausal solutions, one of which is already known from the literature. By modifying this operation, phase-splitting systems are obtained, one of them related to corresponding continuous ones, discussed in papers published around 1950. Another system with approximately linear phase corresponds to a paper presented in 1987. Finally, the coupled form of these phase splitting allpasses is found to be a Hilbert transformer with precise phase difference, but with deviations of the magnitudes of the frequency responses.
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    Computationally efficient, robust algorithm for matched field processing (1998)
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    Circuits, systems and signal processing 17 (1998), S. 165-193 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The matched field processing (MFP) localization performance of very low frequency (VLF) arrays operated in the deep ocean basins appears to be limited more by uncertainty in the sound velocity profile (SVP) than by low signal-to-noise ratio (SNR). We present a new robust variation of MFP designed to be less sensitive to velocity error in weakly inhomogeneous environments. We analyze the computational requirements of this and other MFP algorithms. When either the search volume is large of the acoustic array is large, computational efficiency is an issue. We present an efficient MFP implementation for the conventional MFP algorithm and our robust algorithm. We show that parallel implementation of these algorithms may allow real-time performance.
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    Global asymptotic stability of a class of feedback neural networks with an application to optimization problems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 219-241 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract By applying results from homotopy theory, new conditions are obtained for the existence and uniqueness of an equilibrium for a class of continuous-time feedback neural networks which contains the Hopfield model as a special case. Next, new criteria are established for the global asymptotic stability of the unique equilibrium of this class of neural networks by utilizing Lur'e-type Lyapunov functions and the stability theory for systems of differential inequalities. Several practical stability testing conditions are given. As a special case, criteria are derived for the global asymptotic stability of Hopfield neural networks. This is followed by a robustness analysis of the class of neural networks considered. The results obtained are then applied to an optimization problem.
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    Optimal interpolating and smoothing functional artificial neural networks (FANNs) based on a generalized fock space framework (1998)
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    Circuits, systems and signal processing 17 (1998), S. 271-287 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Functional artificial neural networks (FANNs) are artificial neural networks (ANNs) in which the synaptic weights are “functions” rather than numbers. Thus the signals in such networks are analog, and the action of a synapse on a signal passing through it takes place in the form of a scalar product inL 2 between the functional weight and the signal. In this paper, four classes of FANNs are introduced. They result from the solution of a nonparametric optimization problem in a generalized Fock space (GFS) of abstract Volterra series under interpolating or smoothing input-output training data constraints. Two of these classes of FANNs correspond to the interpolating case and are represented by what we call the (two-layer)optimal interpolating (OI) FANN and theoptimal multilayer neural interpolating (OMNI) FANN. The remaining two classes correspond to the smoothing case. We name their representations as the (two-layer)optimal smoothing (OS) FANN and theoptimal smoothing multilayer artificial neural (OSMAN) FANN. In addition to providing the background and the derivation of these FANNs, this paper presents a novel approach to their implementation. This approach does away with the computationally cumbersome use of functional weights. Instead, the effect of these weights is provided by linear time-invariant differential equation models of which those weights are impulse responses. These are implemented by a linear filter bank. This approach thus leads to simple and meaningful causal realizations of FANNs which we call Dynamical FANNs or simply D-FANNs.
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    URL: http://dx.doi.org/10.1007/BF01202856
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    Are analog neural networks better than binary neural networks? (1998)
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    Circuits, systems and signal processing 17 (1998), S. 243-270 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper, we study the problem of maximizing an objective function over the discrete set {−1, 1} n using a neural network. It is now known that a binary (two-state) Hopfield network can take, in the worst case, an exponential number of time steps to find even a local maximum of the objective function. In this paper, we carry this argument further by studying theradius of attraction of the global maxima of the objective function. If a binary neural network is used, in general there is no guarantee that a global maximum has a nonzero radius of attraction. In other words, even if the optimization process is started off with the neural network in an initial state that isadjacent to the global maximum, the resulting trajectory of the network may not converge to the nearby maximum, but may instead go off to another maximum. At the same time, another set of recent results shows that, if ananalog neural network is used to optimize the same objective function, thenevery local maximum of the objective function has a nontrivial domain of attraction, and conversely, the only equilibria that are attractive are the local maxima of the objective function. This raises the question as to whether analog neural networks offer some advantages over binary neural networks for optimizing the same objective function. As a motivation for this line of inquiry, we study the problem of decoding an algebraic block code using a neural network. It is shown that the binary neural network implementation has the undesirable property thatall the global maxima of the objective function have azero radius of attraction. In contrast, if an analog neural network is used to maximize exactly the same objective function, the region of attraction of each maximum contains not only the associated “orthant” of the state space, but also some points not in this orthant. In other words, the analog implementation exhibits the desired tolerance to transmission errors, whereas the binary neural network does not have this property. With this motivation, two open questions are posed that provide a program of research for studying the possible superiority of analog neural networks over binary neural networks.
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    Average power analysis of sequential circuits using an autoregressive model (1998)
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    Circuits, systems and signal processing 17 (1998), S. 289-304 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We present a new statistical technique for average power estimation in sequential circuits. Because of the feedback loops, power dissipations of sequential circuits in consecutive clock cycles are temporally correlated. The existence of data correlation makes it unsuitable to apply conventional techniques to average power inference, because the sample variance is no longer a maximum likelihood estimator. The convergence criterion derived from the biased variance estimation will be overly optimistic, causing power simulation to stop prematurely at a lower-than-specified estimation accuracy. To overcome this problem, we propose a systematic approach for modeling the power dissipation behavior of sequential circuits as an autoregressive random process. An accurate process variance can be obtained by the model parameters, which enables the derivation of a robust confidence interval of the average power. The interval is checked for convergence against a user-specified accuracy criterion. An iterative procedure is developed to invoke these steps repeatedly until the convergence specification is met. For a set of benchmark sequential circuits, this technique yields high accuracy and efficiency.
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    An algebraic technique for designing active filters in the frequency domain for control and signal processing (1998)
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    Circuits, systems and signal processing 17 (1998), S. 391-400 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a straightforward algebraic method for designing feedback loops in the frequency domain. The emphasis here is on control system design, but the technique is applicable to active filter design as well. The object is to produce a practical analog filter with a minimum of design effort. The algebraic solution to the design problem is presented, and several examples are explored.
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    Parameter estimation using RELAX with a COLD array (1998)
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    Circuits, systems and signal processing 17 (1998), S. 471-481 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This correspondence presents a RELAX (RELAXation-based) algorithm for angle, polarization, and waveform estimation of completely polarized narrowband electromagnetic plane waves arriving at a uniform linear co-centered orthogonal loop and dipole (COLD) array. We use numerical examples to demonstrate the performance of the RELAX algorithm for parameter estimation with the COLD array and compare it with the performance of the MODE (Method of Direction Estimation) algorithm. We show that this RELAX algorithm can outperform MODE and yet be computationally faster than MODE.
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    Coordinate logic filters and their applications in image processing and pattern recognition (1998)
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    Circuits, systems and signal processing 17 (1998), S. 517-538 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we present a number of image processing applications using coordinate logic filters, which execute coordinate logic operations among the pixels of the image. These filters are very efficient in various 1D, 2D, or higher-dimensional digital signal processing applications, such as noise removal, magnification, opening, closing, skeletonization, and coding, as well as in edge detection, feature extraction, and fractal modeling. In this paper we present some typical image processing applications using coordinate logic filters. The key issue in the coordinate logic analysis of images is the method of fast successive filtering and managing of the residues. The desired processing is achieved by executing only direct logic operations among the pixels of the given image. Coordinate logic filters can be easily and quickly implemented using logic circuits or cellular automata; this is their primary advantage.
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    Discretization of cascaded continuous-time controllers and uncertain systems (1998)
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    Circuits, systems and signal processing 17 (1998), S. 591-611 
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    ISSN: 1531-5878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper presents a new method for the digital modeling of a continuous-time uncertain system and a new method for the digital redesign of a sampled-data uncertain system. The system matrices characterizing the state-space representation of the original uncertain system are assumed to be interval matrices. The Chebyshev quadrature formula together with the interval arithmetic are used for the digital interval modeling, and a dual concept of digital interval modeling is utilized to discretize a predesigned cascaded analog controller for robust digital control of a continuous-time uncertain system. Using the newly developed digital interval models and digitally redesigned controllers, the resulting dynamic states of the digitally controlled sampled-data uncertain systemsare able to closely match those of the originally analogously controlled continuous-time uncertain systems for a relatively longer sampling period.
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    URL: http://dx.doi.org/10.1007/BF01203107
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    Eyes Closed: Simple, Intuitive, Statistically Sound, and Efficient Methods for Estimating Parameters of Clonal Growth Cancer Models (1998)
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    Risk analysis 18 (1998), S. 529-534 
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    ISSN: 1539-6924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
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    URL: http://dx.doi.org/10.1023/B:RIAN.0000006255.30436.ff
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    A Risk Assessment for Consumers of Mourning Doves (1998)
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    Risk analysis 18 (1998), S. 563-573 
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    ISSN: 1539-6924
    Keywords: Risk assessment ; mourning doves ; hunting ; radionuclides ; heavy metals ; lead shot ; cesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Recreational and subsistence hunters and anglers consume a wide range of species, including birds, mammals, fish and shellfish, some of which represent significant exposure pathways for environmental toxic agents. This study focuses on the Department of Energy's (DOE's) Savannah River Site (SRS), a former nuclear weapons production facility in South Carolina. The potential risk of contaminant intake from consuming mourning doves (Zenaida macroura), the most popular United States game bird, was examined under various risk scenarios. For all of these scenarios we used the mean tissue concentration of six metals (lead, mercury, cadmium, selenium, chromium, manganese) and radiocesium, in doves collected on and near SRS. We also estimated risk to a child consuming doves that had the maximum contaminant level. We used the cancer slope factor for radiocesium, the Environmental Protection Agencies Uptake/Biokinetic model for lead, and published reference doses for the other metals. As a result of our risk assessments we recommend management of water levels in contaminated reservoirs so that lake bed sediments are not exposed to use by gamebirds and other terrestrial wildlife. Particularly, measures should be taken to insure that the hunting public does not have access to such a site. Our data also indicate that doves on popular hunting areas are exposed to excess lead, suggesting that banning lead shot for doves, as has been done for waterfowl, is desirable.
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    An Empirical Approach for Deriving Information on Total Duration of Exposure from Information on Historical Exposure (1998)
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    Risk analysis 18 (1998), S. 611-619 
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    ISSN: 1539-6924
    Keywords: Exposure duration ; survey data ; longevity bias ; angler populations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Exposure duration is an important component in determining long-term dose rates associated with exposure to environmental contaminants. Surveys of exposed populations collect information on individuals' past behaviors, including the durations of a behavior up to the time of the survey. This paper presents an empirical approach for determining the distribution of total durations that is consistent with the distribution past durations obtained from surveys. This approach is appropriate where the rates of beginning and ending a behavior are relatively constant over time. The approach allows the incorporation of information on the distribution of age in a population into the determination of the distribution of durations. The paper also explores the impact of “longevity” bias on survey data. A case study of the application of this approach to two angler populations is also provided. The results of the case study have characteristics similar to the results reported by Israeli and Nelson (Risk Anal. 12, 65–72 (1992)) from their analytical model of residential duration. Specifically, the average period of time for the total duration in the entire population is shorter than the average period of time reported for historical duration in the surveyed individuals.
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    A Quantitative Test of the Cultural Theory of Risk Perceptions: Comparison with the Psychometric Paradigm (1998)
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    Risk analysis 18 (1998), S. 635-647 
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    ISSN: 1539-6924
    Keywords: Risk perceptions ; cultural theory ; psychometric paradigm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract This paper seeks to compare two frameworks which have been proposed to explain risk perceptions, namely, cultural theory and the psychometric paradigm. A structured questionnaire which incorporated elements from both approaches was administered to 129 residents of Norwich, England. The qualitative risk characteristics generated by the psychometric paradigm explained a far greater proportion of the variance in risk perceptions than cultural biases, though it should be borne in mind that the qualitative characteristics refer directly to risks whereas cultural biases are much more distant variables. Correlations between cultural biases and risk perceptions were very low, but the key point was that each cultural bias was associated with concern about distinct types of risks and that the pattern of responses was compatible with that predicted by cultural theory. The cultural approach also provided indicators for underlying beliefs regarding trust and the environment; beliefs which were consistent within each world view but divergent between them. An important drawback, however, was that the psychometric questionnaire could only allocate 32% of the respondents unequivocally to one of the four cultural types. The rest of the sample expressed several cultural biases simultaneously, or none at all. Cultural biases are therefore probably best interpreted as four extreme world views, and a mixture of qualitative and quantitative research methodologies would generate better insights into who might defend these views in what circumstances, whether there are only four mutually exclusive world views or not, and how these views are related to patterns of social solidarity, and judgments on institutional trust.
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    Unemployment insurance: Risk sharing versus efficiency (1991)
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    The Geneva risk and insurance review 16 (1991), S. 59-74 
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    ISSN: 1554-9658
    Keywords: Unemployment Insurance ; Risk Sharing ; Social Security
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract Two models of spot labor markets are presented in which labor suppliers have heterogeneous attitudes towards effort and in which uncertainty prevails on labor productivity and growth. The problem of selecting efficient rules to manage unemployment insurance (UI) systems is considered. We show that there does not exist any system which combines an efficient allocation of labor with an efficient allocation of risks among employees, unemployed workers and capital-owners. Pareto-efficient policy rules are a best compromise between these two conflicting objectives. It implies that productive efficiency could be improved in periods of mass unemployment by reducing UI benefits. That would be at the expense of more inefficiencies in the sharing of macroeconomic risks. At the optimum, the UI benefit is positively correlated to growth and it is negatively correlated to labor productivity.
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    A comment on social insurance (1991)
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    The Geneva risk and insurance review 16 (1991), S. 137-138 
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    ISSN: 1554-9658
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
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    A comment on Professor Atkinson's lecture (1991)
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    The Geneva risk and insurance review 16 (1991), S. 139-141 
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    ISSN: 1554-9658
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
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    Incentives, redistribution and social insurance (1991)
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    The Geneva risk and insurance review 16 (1991), S. 143-165 
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    ISSN: 1554-9658
    Keywords: Social Insurance ; Redistribution ; Incentives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract We extend the familiar income taxation model à la Mirrlees, so as to include income uncertainty, due for instance to a risk of illness. Following a line of research initiated by Blomqvist and Horn [1984] we prove that the existence of a Social Health Insurance system may be justified even when the insurance market is efficient. Moreover, if there is a negative statistical dependence between probability of illness and labor productivity, then the optimum of a Utilitarianist Social Welfare function implies that Social Insurance provides a complete coverage for every household.
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    Risk taking and taxation in complete capital markets (1991)
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    The Geneva risk and insurance review 16 (1991), S. 167-177 
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    ISSN: 1554-9658
    Keywords: Risk Taking ; Taxation ; Complete Conventional Securities Markets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Notes: Abstract In general equilibrium, with complete conventional securities markets and endogenous asset supply, taxes on risk remuneration are ineffective but harmless. They do not alter the real allocation of goods or the distribution of wealth, they impose no excess burden, and, in particular, have no impact on risk taking.
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    Bioconversion of the sodium salt of Simvastatin (MK-733) to 6-desmethyl-6-α-hydroxymethyl Simvastatin (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 157-164 
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    ISSN: 1476-5535
    Keywords: Actinomycete ; Biotransformation ; pH control ; Magnesium sulfate ; MK-733 ; Simvastatin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary An actinomycete (MA 6474, ATCC 53828) isolated from a soil sample (Mutare, Zimbabwe) was found to biotransform the sodium salt of Simvastatin (MK-733) to 6-α-hydroxymethyl MK-733, 6-β-hybroxymethyl MK-733, and 6-ring-hydroxy MK-733. The bioconversion efficiency to the desired compound, 6-α-hydroxymethyl MK-733, was enhanced by optimizing the physico-chemical parameters of the process. In shake flask cultures, addition of magnesium (0.125 mg/l Mg SO4·7H2O) to the medium resulted in a five-fold increase in the rate of bioconversion to the α diastereomer. The ratio of bioconversion products (6-α-hydroxymethyl, 6-β-hydroxymethyl, and 6-ring-hydroxy MK-733) was regulated by pH. Process improvements and scale up in 23-1 fermentors, which consisted of a controlled addition of substrate (MK-733), resulted in a 2-fold increase in alpha diastereomer Production (42 vs. 79 U/ml) and a 23-fold rate increase in the formation of α-diastereomer. A high diastereomeric ratio (α: β=9∶1) facilitated downstream processing.
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    Fermentation study for the production of hepatitis B virus pre-S2 antigen by the methylotrophic yeastHansenula polymorpha (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 147-156 
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    ISSN: 1476-5535
    Keywords: Methanol ; Yeast extract ; Two-phase process ; Periplasmic antigen ; Intracellular antigen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Various physico-chemical parameters have been studied in order to improve the production of hepatitis B virus pre-S2 antigen (middle surface antigen) by the methylotrophic yeastHansenula polymorpha. Antigen production was done in two steps: first, production of cells on glycerol (Phase 1), followed by induction of antigen expression with methanol (Phase 2). Dense cultures ofH. polymorpha, equivalent to 35–40 g/l (dry weight), were readily obtained in small fermenters using minimal medium containing glycerol as carbon source. Antigen expression in this minimal medium, after induction with methanol, was however low and never exceeded 1.6 mg/l of culture. Antigen production was greatly enhanced by adding complex organic nitrogen sources along with methanol at induction time; yeast extract was the best of all the sources tested. In shake flasks, antigen production was proportional to yeast extract concentration up to 7% (w/v) yeast extract. it became clear that the nutritional conditions for good antigen expression were different from those for good biomass production. The effects of yeast extract were reproduced in small fermenters: antigen levels reached 8–9 mg/l in medium containing 6% (w/v) yeast extract during induction with methanol. The mechanisms of yeast extract's effects are still unknown but are probably nutritional. The recombinantH. polymorpha strain produced both periplasmic and intracellular antigen. The periplasmic antigen was shown to be present as 20–22-nm particles and was therefore immunogenic. Immunoblotting indicated that part of the pre-S2 antigen was present as a 24-kDa degradation product. These studies have led to a 140-fold increase in volumetric productivity of antigen and to a 4.6-fold increase in specific production.
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    Effect of cultural conditions on production of eicosapentaenoic acid byPythium irregulare (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 171-178 
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    ISSN: 1476-5535
    Keywords: EPA ; Omega-3 ; Arachidonic acid ; Polyunsaturated fatty acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The effect of culture conditions upon lipid content and fatty acid composition of mycelia ofPythium irregulare was investigated with particular attention to increasing the yield of 5,8,11,14,17-eicosapentaenoic acid (20∶5; ω−3) (EPA). All experiments were done by shake flask culture using a yeast extract + malt extract medium. The maximum growth rate was obtained at 25°C, but maximum EPA production was obtained at 12°C. The highest EPA production was 76.5 μg EPA/ml 13 days fermentation at 12°C. Addition of glucose during fermentation increased the yield considerably. The highest yield was 112 μg/ml, obtained at 13 days fermentation with spiking on day 11. Fermentation time could be shortened by initial incubation at 25°C for 2 days, followed by incubation at 12°C for 6 days. The culture also produced arachidonic acid and other ω-6 polyunsaturated fatty acids. EPA production was also obtained with lactose or sweet whey permeate, a by-product of cheese manufacture that contains lactose as the main carbohydrate.
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    Production of arachidonic acid byMortierella alpina ATCC 32222 (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 179-185 
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    ISSN: 1476-5535
    Keywords: Mortierella alpina ; Arachidonic acid ; Polyunsaturated fatty acid ; Fungal lipid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary WhenMortierella alpina ATCC 32222 was incubated in a glucose salts medium at 25°C the biomass (17.5 g/l) contained 9.62% arachidonic acid which amounted to 54% (w/w) of total biomass lipids. When the glucose concentration in the medium was varied from 0 to 150 g/l, the percentage of arachidonic acid in biomass and in lipids was highest at a glucose concentration of 30 g/l, but highest yield of arachidonic acid per litre of culture broth was observed at a glucose concentration of 100 g/l. While production of biomass reached a plateau of 17 g/l after a 3-day incubation at 25°C, the percentage of arachidonic acid in lipids and biomass increased dramatically from 3 to 6 days with a concurrent arachidonic acid yield increase from 0.89 to 1.63 g/l. Optimum initial culture pH for arachidonic acid production was in the range 6.0–6.7. By increasing the concentration of the glucose salts medium three-fold, yields of biomass and arachidonic acid were increased to 35.8 g/l and 3.73 g/l, respectively.
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    Sch 42029, a naturally produced dopamine receptor ligand: Taxonomy, fermentation, isolation and structure (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 187-192 
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    ISSN: 1476-5535
    Keywords: Dopamine receptor ; Agonist and antagonist ; Ligand ; Dihydroxy acetanilide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A natural product, Sch 42029, isolated from the fermentation of anActinoplanes sp. (SCC 1971) was found to displace Sch 23390 from the dopamine-1 (D1) receptor. The compound was isolated from the fermentation broth by adsorption of the filtrate on XAD-16 resin, elution with water-methanol, followed by purification by gel-permeation chromatography and HPLC. Using spectroscopic analysis, the structure was determined to be 2,5-dihydroxy acetanilide. The pure compound displaced Sch 23390, a D1-selective ligand, at aK i of 1.6 μm and spiperone, a D2-selective ligand, at aK i of 200 μm.
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    The assimilation of organic hazardous wastes by municipal solid waste landfills (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 193-199 
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    ISSN: 1476-5535
    Keywords: Organic hazardous waste ; Leachate ; Landfill management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Co-disposal of 12 compounds representing major organic classes (aromatic hydrocarbons, halogenated hydrocarbons, pesticides, phenols, and phthalate esters) with shredded municipal solid waste was tested using a laboratory-scale column and pilot-scale lysimeter to characterize transport and transformation phenomena including sorption, volatilization and bioassimilation. Leachate and gases emitted from the lysimeters were examined for identifiable products of biotransformation. The results of this investigation provided a mechanistic evaluation of the attenuating and assimilative capacity of municipal solid waste landfills for specific organic compounds. Physical/chemical organic compound characteristics were related to refuse characteristics and composition to predict compound fate. Such knowledge is useful in developíng landfill management and operational strategies consistent with the need for control of pollutant releases.
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    Cadmium sorption by bacteria and freshwater sediment (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 201-207 
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    ISSN: 1476-5535
    Keywords: Diffusion chamber ; Cadmium-sensitive ; Cadmium-resitant ; Sediment ; Bacteria ; Cadmium-sorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Sorption of cadmium by sediment bacteria and freshwater sediment was investigated using diffusion chambers to simulate the water-sediment interface. Diffusion chambers were constructed to provide two compartments separated by a dialysis membrane. Diffusion of cadmium across the membrane was monitored after pure cultures of sediment bacteria or lake sediments were added to the sediment side of a diffusion chamber. Cellular accumulation of cadmium by cadmium-sensitive and cadmium-resistant bacteria removed between 20% and 80% of the dissolved cadmium from the simulated water column and pore water. Cellular accumulation of cadmium was greatest for cadmium-sensitive isolates that were tested. Sediment with an intact microbial community sequestered 80% of the cadmium added to sediment, whereas autoclaved sediment retained 97% of the metal that was added. Addition of glucose to cadmium-amended sediment decreased retention of cadmium by untreated and autoclaved sediments, resulting in elevated concentrations of dissolved cadmium in the simulated water column.
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    Determination of chemical biodegradation by direct and indirect methods (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 209-212 
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    ISSN: 1476-5535
    Keywords: Biodegradation ; Direct method ; Indirect method ; Method comparison ; BOD method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Degradation of 10 organic chemicals by pre-acclimated microorganisms in BOD dilution water was determined directly by UV spectrophotometry and indirectly by a modified BOD method. Residual chemical concentrations were periodically measured and pseudo-first-order biodegradation rate constants (k 1) were calculated. Thek 1 spectrophotometry values ranged from 0.006/h to 0.077/h andk 1-BOD values from 0.002/h to 0.043/h for 1-methylnaphthalene and indole, respectively. The ratios ofk spectrophotometry to k1-BOD were between 1.5 for salicylic acid and 3.0 for 1-methylnaphthalene with a mean of 2.7. A significant (α=0.001) linear correlation (r 2=0.854,F=46.630) existed between the two sets of rate constants. Results from this study suggest that the modified BOD method may be used to estimate chemical biodegradation rates in synthetic media.
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    Biofilms: An ESEM evaluation of artifacts introduced during SEM preparation (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 213-221 
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    ISSN: 1476-5535
    Keywords: Biofilm ; Scanning electron microscope ; Environmental scanning electron microscope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Descriptions of biofilms and their elemental compositions based on scanning electron micrographs and energy dispersive x-ray analysis cannot be related to the original condition of the biofilm on the surface. Solvent replacement of water removes extracellular polymeric material and reduces the concentration of elements bound within the biofilm. In the wet state, bacteria and microalgae are enmeshed in a gelatinous film that is either removed or dried to a thin inconspicuous residue during sample preparation for scanning electron microscopy. The environmental scanning electron microscope provides a fast, accurate image of biofilms, their spatial relationship to the substratum and elemental composition.
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    Oligotrophic bacteria in ultra-pure water systems: Media selection and process component evaluations (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 223-227 
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    ISSN: 1476-5535
    Keywords: Deionized water ; Ultra-pure water ; Ozone ; Ultra-violet sterilization ; Oligotroph ; Bacteria ; R2A medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Presently, tryptic soy agar (TSA) medium is used in the semiconductor industry to determine the concentration of viable oligotrophic bacteria in ultra-pure water systems. Deionized water from an ultra-pure water pilot plant was evaluated for bacterial growth at specific locations, using a non-selective medium (R2A) designed to detect injured heterotrophic as well as oligotrophic bacteria. Results were compared to those obtained using Tryptic Soy Agar. Statistically greater numbers of bacteria were observed when R2A was used as the growth medium. Total viable bacterial numbers were compared both before and after each treatment step of the recirculating loop to determine their effectiveness in removing bacteria. The reduction in bacterial numbers for the reverse osmosis unit, the ion exchange bed, and the ultraviolet sterilizer were 97.4%, 31.3%, and 72.8%, respectively, using TSA medium, and 98.4%, 78.4%, and 35.8% using R2A medium. The number of viable bacteria increased by 60.7% based on TSA medium and 15.7% based on R2A medium after passage of the water through an in-line 0.2-μm pore size nylon filter, probably because of the growth of bacteria on the filter. Our results suggest that R2A medium may give a better representation of the microbial water quality in ultra-pure water systems and therefore a better idea of the effectiveness of the various treatment processes in the control of bacteria.
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    Studies on the galactomannan-degrading enzymes produced bySporotrichum cellulophilum (1991)
    Springer
    Journal of industrial microbiology and biotechnology 8 (1991), S. 229-236 
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    ISSN: 1476-5535
    Keywords: Mannanase ; Sporotrichum cellulophilum ; Galactomannan ; Hemicellulase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Extracellular mannanase activity produced bySporotrichum cellulophilum was purified into two components using acetone precipitation, SP-Sephadex C50 ion exchange chromatography and preparative polyacrylamide gel electrophoresis. The purified mannanse components, M1 and M2, had molecular weights of 108 000–112 000 and 32 200–36 000 respectively. Component M1 was shown to contain 2 subunits having molecular weights of 62 000 and 50 000. M1 and M2 had similar pH-activity profiles with pH optima of 5.5 and 6.0 respectively. M1 was more thermostable than M2: half lives of the enzymes at 70°C were 30 and 9 min for M1 and M2 respectively.
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    Emulsification of hydrocarbons by subsurface bacteria (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 237-245 
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    ISSN: 1476-5535
    Keywords: Microbial emulsifier ; Biosurfactant ; Bioemulsifier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Biosurfactants have potential for use in enhancement of in situ biorestoration by increasing the bioavailability of contaminants. Microorganisms isolated from biostimulated, contaminated and uncontaminated zones at the site of an aviation fuel spill and hydrocarbon-degrading microorganisms isolated from sites contaminated with unleaded gasoline were examined for their abilities to emulsify petroleum hydrocarbons. Emulsifying ability was quantified by a method involving agitation and visual inspection. Biostimulated-zone microbes and hydrocarbon-degrading microorganisms were the best emulsifiers as compared to contaminated and uncontaminated zone microbes. Biostimulation (nutrient and oxygen addition) may have been the dominant factor which selected for and encouraged growth of emulsifiers; exposure to hydrocarbon was also important. Biostimulated microorganisms were better emulsifiers of aviation fuel (the contaminant hydrocarbon) than of heavier hydrocarbon to which they were not previously exposed. By measuring surface tension changes of culture broths, 11 out of 41 emulsifiers tested were identified as possible biosurfactant producers and two isolates produced large surface tension reductions indicating the high probability of biosurfactant production.
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    The effect of pretreatment on the invertase activity of gel-entrapped yeast biomass (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 247-252 
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    ISSN: 1476-5535
    Keywords: Invertase ; Entrapped yeast ; Ethanol pretreatment ; Heat pretreatment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Gel-entrapped, non-viable yeast biomass with specific invertase activity has been produced by two different pretreatment protocols: a short-time thermal treatment and a brief contact with concentrated ethanol solutions. Four yeast strains were most promising:K. fragilis L-293,C. utilis L-282,S. cerevisiae L-170 and L-209. Of these, the ethanol-tolerant L-282 and the ethanol-tolerant and heat-resistant L-170 gave the most active gel-entrapped biocatalysts: around 2 mg of reducing sugars produced per mg dry yeast per min.
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    Expression of streptomycete cholesterol oxidase inEscherichia coli (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 253-258 
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    ISSN: 1476-5535
    Keywords: Cholesterol ; 4-Cholesten-3-one ; Cholesterol oxidation ; Heterologous gene expression ; Streptococcal vector
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A streptomycete gene coding for extracellular cholesterol oxidase (choA) was subcloned and expressed inEscherichia coli. The pUCO series recombinants were obtained by inserting thechoA gene into the uniqueKpnI site of pUC19 vector. Expression was observed with pUCO192A and pUCO193 constructs in which the cloned gene(s) were aligned with the upstreamlacZ promoter. Isopropyl β-d-thioglucopyranoside (IPTG) enhanced this expression up to 2.5-fold. Specific Cho activity in the cell extracts of the stable pUCO193 transformant were 0.004 U and 0.007 U per mg protein without and with IPTG induction, respectively. Cho activity was detected in the spent medium of this culture, suggesting possible secretion of the enzyme.
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    Resistance of bacteria from cooling waters to bactericides (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 273-276 
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    ISSN: 1476-5535
    Keywords: Bacterial resistance ; Isothiazolone, Quarternary ammonium compounds ; Thiocarbamate ; Water cooling system ; Pseudomonas cepacia ; Pseudomonas stutzeri ; Bacillus subtilis ; Bacillus cereus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Bacteria from water cooling systems developed resistance to three different bactericides i.e. quarternary ammonium compound (QAC), isothiazolone and thiocarbamate. Resistance was induced by exposing isolates to increasing sublethal concentrations for a period of 10 weeks.Bacillus subtilis became resistant to 1000 mg l−1 QAC. Cross-resistance was also detected, e.g. isothiazolone induced resistance to QAC and thiocarbamate.
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    The biosynthetic origin of the pyridone ring of efrotomycin (1991)
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    Journal of industrial microbiology and biotechnology 8 (1991), S. 265-271 
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    ISSN: 1476-5535
    Keywords: Efrotomycin ; Nocardia lactamdurans ; Uracil catabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Nocardialactamdurans has been shown to catabolyse uracil via the reductive pathway. The end product of this pathway, β-alanine, is incorporated into the pyridone ring of efrotomycin. Support for this proposal includes: (1) reversal of thymine inhibition of efrotomycin biosynthesis by dihydrouracil andN-carbamoyl-β-aline, two intermediates of the catabolic pathway; (2) incorporation of [5,6-3H]-uracil into efrotomycin with a relative molar specific activity of approximately 0.5, close to the theoretical maximum; and (3)13C coupling at C4 and C5 of efrotomycin after feeding resting cells with [4,5-13C]-uracil. Our results do not rule out the possibility of an alternative source of β-alanine or the coexistence of uracil catabolism via oxidative reactions.
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    Book reviews (1998)
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    Bulletin of mathematical biology 60 (1998), S. 597-613 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1997.0004
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    Kinetic and thermodynamic principles determining the structural design of ATP-producing systems (1998)
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    Bulletin of mathematical biology 60 (1998), S. 505-543 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract It is theoretically analysed whether the structural design of ATP-producing pathways, in particular the design of glycolysis, may be explained by optimization principles. On the basis of kinetic and thermodynamic principles conclusions are derived concerning the stoichiometry of these pathways in states of high ATP production rates. One of the extensions to previous investigations is that the concentrations of the adenine nucleotides are taken into account as variable quantities. This necessitates the consideration of an interaction of the ATP-producing system I with an external ATP-consuming system II. A great variety of pathways is studied which differ in the number and location of ATP-consuming reactions, ATP-producing reactions and reactions involving inorganic phosphate. The corresponding number of possible pathways may be calculated in an explicit manner as a function of the number of those reactions which do not couple to ATP or inorganic phosphate. The kinetics of the individual reactions are described by linear or bilinear functions of reactant concentrations and all rate equations are expressed in terms of equilibrium constants and characteristic times. A thermodynamical analysis of the two coupled systems yields upper and lower limits for the concentration of ATP and an explicit expression for the maximal difference between the number of ATP-producing and ATP-consuming reactions of system I. The following results of the optimization are obtained. (i) The ATP production rate always increases if the ATP-producing reactions as well as those reactions characterized by an uptake of inorganic phosphate are shifted as far as possible towards the end of system I. (ii) Explicit conditions for the optimal location of the ATP-consuming reactions are presented. The results are discussed in the context of characteristic times as well as in terms of enzyme kinetic parameters. (iii) For two sets of characteristic times the resulting stoichiometries and their corresponding steady-state fluxes are investigated in detail. One of these stoichiometries shows a close correspondence to contemporary standard glycolysis. (iv) It is shown that most possible pathways result in a very low steady-state flux, that is, the optimal stoichiometry is characterized by a significant selective advantage. (v) The standard free energy profile of a pathway with an optimal stoichiometry is discussed. It differs significantly from the free energy profiles of nonoptimized pathways.
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    Limiting models for calcification in fibrous tissues adjacent to orthopedic implants: Variational indicator functions and influences of implant stiffness (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 615-646 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Calcification and eventual integration of orthopedic implants into bone is important to many load-bearing devices, and the influence of load and implant stiffness on this process are assessed in this mathematical modelling study. Three research questions are posed in this study. First, can limiting material models provide useful information on the overall behavior of the tissue adjacent to a loaded orthopedic implant? Second, can the limiting models lead to optimization criteria? Third, can an optimization approach be used to differentiate between the four prospective remodeling rate equations which are proposed? The answers are yes, yes, and no, respectively. A two degree of freedom lumped parameter model for axial loading of an intramedullary implant is considered. Two limiting composite material models are used, and the strain energy density in the calcified and non-calcified phases are assessed as stimuli for calcification. The rate equations posed here assume that the calcified material volume fraction decreases at high strain-energy densities, and increases at small strain-energy densities. In all four cases (both models, both phases) the steady states for these rate equations find equilibrium points of indicator functions which are a weighted sum of total strain energy and the mass of calcified tissue in the layer considered. The weights on strain-energy density and mass differ in each case. This shows that for appropriate choices of parameters, all four models can yield the same results, and it also shows that an optimization approach does not uniquely determine the appropriate rate equation in these cases. The rate equations showed complicated dynamic behavior and a phase-plane analysis was used which led to upper bounds on load, which depended on implant stiffness and distal support. The predictions of the four cases studied are compared.
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    Food chains in the chemostat: Relationships between mean yield and complex dynamics (1998)
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    Bulletin of mathematical biology 60 (1998), S. 703-719 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Atritrophic food-chain chemostat model composed of a prey with Monod-type nutrient uptake, a Holling Type II predator and a Holling Type II exploited superpredator is considered in this paper. The bifurcations of the model show that dynamic complexity first increases and then decreases with the nutrient supplied to the bottom of the food chain. Extensive simulations prove that the same holds for food yield, i.e., there exists an optimum nutrient supply which maximizes mean food yield. Finally, a comparative analysis of the results points out that the optimum nutrient supply practically coincides with the nutrient supply separating chaotic dynamics from high-frequency cyclic dynamics. This reinforces the idea, already known for simpler models, that food yield maximization requires that the system behaves on the edge of chaos.
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    A non-stochastic approach for modeling uncertainty in population dynamics (1998)
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    Bulletin of mathematical biology 60 (1998), S. 721-751 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We developed a non-stochastic methodology to deal with the uncertainty in models of population dynamics. This approach assumed that noise is bounded; it led to models based on differential inclusions rather than stochastic processes, and avoided stochastic calculus. Examples of estimations of extinction times for exponential and logistic population growth with environmental and demographic noise are presented.
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    Designing metabolism: Alternative connectivities for the pentose phosphate pathway (1998)
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    Bulletin of mathematical biology 60 (1998), S. 815-856 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We present a method for generating alternative biochemical pathways between specified compounds. We systematically generated diverse alternatives to the nonoxidative stage of the pentose phosphate pathway, by first finding pathways between 5-carbon and 6-carbon skeletons. Each solution of the equations for the stoichiometric coefficients of skeleton-changing reactions defines a set of networks. Within each set we selected networks with modules; a module is a coupled set of reactions that occurs more than one in a network. The networks can be classified into at least 53 families in at least seven superfamilies, according to the number, the input-output relations, and the internal structure of their modules. We then assigned classes of enzymes to mediate transformations of carbon skeletons and modifications of functional groups. The ensemble of candidate networks was too large to allow complete determination of the optimal network. However, among the networks we studied the real pathway is especially favorable in several respects. It has few steps, uses no reducing or oxidizing compounds, requires only one ATP in one direction of flux, and does not depend on recurrent inputs.
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    Intratrophic predation in simple predator-prey models (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 937-953 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Intratrophic predation is a phenomenon not usually considered in mathematical models of biological populations, and yet it may occur in any model where many species are considered as a single model variable. This paper demonstrates how intratrophic predation can be rationally included in a general predator-prey model, and shows that the resulting model has some desirable and intuitively plausible features. A simple asymptotic method is developed in order to investigate how intratrophic predation can affect both the position and stability of the equilibria of a model. The methods can be applied to wide classes of population models, and the conclusions drawn are of practical importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0053
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  • 99
    Electronic Resource
    Electronic Resource
    Probability density functions useful for parametrization of heterogeneity in growth and allometry data (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 1099-1122 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract This paper addresses the problem of modelling heterogeneous individual characteristics in a population. A flexible unified approach for stochastic parametrization dynamics of the distribution in population data is proposed. To approximate data with multiple observations per individual, models based on Markov processes are constructed. The method can be applied to scalar or multivariate characteristics, and its application to growth and allometry data is considered. Different stochastic versions of known growth and allometry functions are developed, which enable wide applicability. Simple informative growth indices are calculated as the moments of distribution. The three-parameter Gompertz growth model for size-at-age data was reparametrized to a size-increment data model with two parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0058
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  • 100
    Electronic Resource
    Electronic Resource
    A Bayes-optimal sequence-structure theory that unifies protein sequence-structure recognition and alignment (1998)
    Springer
    Bulletin of mathematical biology 60 (1998), S. 1039-1071 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A rigorous Bayesian analysis is presented that unifies protein sequence-structure alignment and recognition. Given a sequence, explicit formulae are derived to select (1) its globally most probable core structure from a structure library; (2) its globally most probable alignment to a given core structure; (3) its most probable joint core structure and alignment chosen globally across the entire library; and (4) its most probable individual segments, secondary structure, and super-secondary structures across the entire library. The computations involved are NP-hard in the general case (3D-3D). Fast exact recursions for the restricted sequence singleton-only (1D-3D) case are given. Conclusions include: (a) the most probable joint core structure and alignment is not necessarily the most probable alignment of the most probable core structure, but rather maximizes the product of core and alignment probabilities; (b) use of a sequence-independent linear or affine gap penalty may result in the highest-probability threading not having the lowest score; (c) selecting the most probable core structure from the library (core structure selection or fold recognition only) involves comparing probabilities summed over all possible alignments of the sequence to the core, and not comparing individual optimal (or near-optimal) sequence-structure alignments; and (d) assuming uninformative priors, core structure selection is equivalent to comparing the ratio of two global means.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/S0092-8240(98)90002-7
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