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  • Springer  (55,483)
  • 2015-2019
  • 1985-1989  (55,483)
  • 1988  (55,483)
  • 1
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    Bulletin of mathematical biology 50 (1988), S. 35-41 
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A dynamical model of the left ventricle as a thick-walled cylinder contracting radially is used to derive the P-V (pressure-volume) relation in the left ventricular cavity during contraction. It is shown how the mathematical results derived could apply to experimental results.
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    Bulletin of mathematical biology 50 (1988), S. 67-75 
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    Notes: Abstract We give conditions for local and global stability of discrete one-dimensional population models. We give a new test for local stability when the derivative is −1. We give several sufficient conditions for global stability. We use these conditions to show that local and global stability coincide for the usual models from the literature and even for slightly more complicated models. We give population models, which are in some sense the simplest models, for which local and global stability do not coincide.
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    Bulletin of mathematical biology 50 (1988), S. 97-120 
    ISSN: 1522-9602
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    Notes: Abstract We consider efficient methods for computing a difference metric between two sequences of symbols, where the cost of an operation to insert or delete a block of symbols is a concave function of the block's length. Alternatively, sequences can be optimally aligned when gap penalties are a concave function of the gap length. Two algorithms based on the ‘candidate list paradigm’ first used by Waterman (1984) are presented. The first computes significantly more parsimonious candidate lists than Waterman's method. The second method refines the first to the point of guaranteeingO(N 2 lgN) worst-case time complexity, and under certain conditionsO(N 2). Experimental data show how various properties of the comparison problem affect the methods' relative performance. A number of extensions are discussed, among them a technique for constructing optimal alignments inO(N) space in expectation. This variation gives a practical method for comparing long amino sequences on a small computer.
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    Bulletin of mathematical biology 50 (1988), S. 187-192 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract It is well documented, in the biological literature, that many species throughout the animal kingdom exhibit Gompertzian or Weibull-like population level total survival distributions. Many researchers have long assumed, believed, or otherwise postulated that an individual organism, in such a population, survived according to an exponential survival distribution. Using well-known results from reliability theory, it is shown that if every individual in the population has an exponentially distributed lifespan, then a Gompertzian or Weibull-like group/population level dynamics (or any other dynamics with a strictly increasing mortality rate for some interval) is not possible. This implies that, for species with a population level Gompertzian or Weibull (with the mortality rate strictly increasing) survival curve, some or all of the individual organisms must have non-exponentially distributed lifespans.
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    Bulletin of mathematical biology 50 (1988), S. 209-225 
    ISSN: 1522-9602
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    Notes: Abstract In flow cytometric measurement of cell DNA distribution one of the major problems is accounting for the effect of fragmentation in the staining process. This work considers a recent probabilistic model that has been proposed for the fragmentation process and species under which conditions it is possible to uniquely identify the DNA distributions of the original population using flow cytometric data. Attention is given both to the normal and to the polyploid case.
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    Bulletin of mathematical biology 50 (1988), S. 379-409 
    ISSN: 1522-9602
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    Notes: Abstract The nonlinear behavior of a particular Kolmogorov-type exploitation differential equation system assembled by May (1973,Stability and Complexity in Model Ecosystems, Princeton University Press) from predator and prey components developed by Leslie (1948,Biometrica 35, 213–245) and Holling (1973,Mem. Entomol. Soc. Can. 45, 1–60), respectively, is re-examined by means of the numerical bifurcation code AUTO 86 with model parameters chosen appropriately for a temperature dependent mite interaction on fruit trees. The most significant result of this analysis is that, in addition to the temperature ranges over which the single community equilibrium point of the system iseither globally stableor gives rise to a globally stable limit cycle, there can also exist a range wherein multiple stable states occur. These stable states consist of a focus (spiral point) and a limit cycle, separated from each other in the phase plane by an unstable limit cycle. The ecological implications of such metastability, hysteresis and threshold behavior for the occurrence of outbreaks, the persistence of oscillations, the resiliency of the system and the biological control of mite populations are discussed. It is further suggested that a model of this sort which possesses a single community equilibrium point may be more useful for representing outbreak phenomena, especially in the presence of oscillations, than the non-Kolmogorov predator-prey systems possessing three community equilibrium points, two of which are stable and the other a saddle point, traditionally employed for this purpose.
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    Bulletin of mathematical biology 50 (1988), S. 493-501 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract This note is concerned with a simple mathematical model of how a population of bacterial spores decrease with time when subjected to a uniform temperature. The model assumes that there is a Boltzman distribution of energy among water or other molecules surrounding the assumed single lethal target in a spore; it assumes that repair is not possible; and that only molecules with energies above a critical level cause inactivation. The model provides new insight concerning the ‘kill-rate’ of spores during ultra heat treatment.
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    Bulletin of mathematical biology 50 (1988), S. 95-95 
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    Bulletin of mathematical biology 50 (1988), S. 143-185 
    ISSN: 1522-9602
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    Notes: Abstract The kinetic theory of neural systems is extended to include the description of cortical-like neural structures. This fact is accomplished by the introduction of long-distance effects. Collaterally, we have the separation of the description of the excitatory activity from that of the inhibitory one. Also, the description of neural systems with a high level of activity is obtained. The modified theory is used to simulate computationally the activity of cortical-like neural systems.
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  • 10
    ISSN: 1522-9602
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    Notes: Abstract A model based upon minimization of surface energy as an explanation for the phenomena of compaction and internalization of cells during mammalian embryo development is generalized for three-dimensional cells. It is shown that, for a spherical embryo, if cells are assumed to be polygonal cones in shape, the simulation of these phenomena for three-dimensional cells is equivalent to simulations of deformations of two-dimensional cells on the surface of a sphere. This equivalence is used to show that in the optimal compacted structure, with no internal cells, the cross-sections of cells in general are not regular polyhedra. Further, the internalization occurs when the number of cells exceeds a critical value which seems to depend on the relative sizes and biophysical properties of cells.
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    Bulletin of mathematical biology 50 (1988), S. 517-530 
    ISSN: 1522-9602
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    Notes: Abstract In previous work (Freedman and Wolkowicz, 1986;Bull. math. Biol. 48, 493–508) it was shown that in a predator-prey system where the prey population exhibits group defence, it is possible that enrichment of the environment could lead to extinction of the predator population. In this paper a third population is introduced and criteria are derived under which persistence of all populations will occur. In particular, criteria for a superpredator and for a competitor to stabilize the system in the sense of persistence are analyzed.
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    Bulletin of mathematical biology 50 (1988), S. 531-545 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract The interaction between osmotic inflow through the wall of a narrow tubule and bulk flow in the tubule is described. Solution are found by a finite difference method, and two approximate analytic solutions are given. Results given here enable more accurate estimates of osmotic permeability to be obtained for the tubule wall. The theory predicts the behaviour of unstirred layers as experimental parameters are varied and enables tubule experiments to be designed so as to reduce unwanted unstirred layer effects.
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    Bulletin of mathematical biology 50 (1988), S. 567-576 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 635-660 
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
    Notes: Abstract Molecular evolution is modelled by erroneous replication of binary sequences. We show how the selection of two species of equal or almost equal selective value is influenced by its nearest neighbours in sequence space. In the case of perfect neutrality and sufficiently small error rates we find that the Hamming distance between the species determines selection. As the error rate increases the fitness parameters of neighbouring species become more and more important. In the case of almost neutral sequences we observe a critical replication accuracy at which a drastic change in the “quasispecies”, in the stationary mutant distribution occurs. Thus, in frequently mutating populations fitness turns out to be an ensemble property rather than an attribute of the individual. In addition we investigate the time dependence of the mean excess production as a function of initial conditions. Although it is optimized under most conditions, cases can be found which are characterized by decrease or non-monotonous change in mean excess productions.
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    Bulletin of mathematical biology 50 (1988), S. 681-696 
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    Notes: Abstract Time-dependent induction of clonal heterogeneity in the neoplastic micro-environment is analysed within the context of a competitive ecology. A model that describes a constant source for clonal emergence was analysed by Michelsonet al. (1987) as an extension of a model proposed by Jansson and Revesz (1974). The extended model has been termed the JRE Model. This paper extends these analyses to time-dependent emergence rates which may represent induction in the presence of a cytotoxic agent. If the analysis is constrained to the tumor micro-environment, and if the emergent subpopulation is drug resistant, then the model may describe the induction and emergence of drug resistant subclones in a growing neoplasm. Asymptotic closed form solutions are derived for a class of emergence rate functions which decay asymptotically to a constant mutation rate. This underlying mutation rate may represent spontaneous mutation to the resistant phenotype, and has been analysed stochastically (Coldmanet al., 1985). The asymptotic solutions to the time-dependent model approach the steady state solution for the JRE Model which represents the dynamics observed in the presence of a constant, spontaneous mutation rate. The clinical and biological implications of these results are discussed.
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    Bulletin of mathematical biology 50 (1988), S. 697-700 
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    Bulletin of mathematical biology 50 (1988), S. 701-701 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Circuits, systems and signal processing 7 (1988), S. 3-19 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we present results in the development of decimation-in-frequency algorithms for a family of discrete sine and cosine transforms. They are closely related to the decimation-in-time algorithms developed by Yip and Rao [1]. The complexity of the algorithms was examined through the number of multiplications and additions as well as the number of different constants required in the transforms. It was found that the decimation-in-frequency approach provides a viable alternative to other fast algorithms for the discrete sine and cosine transforms. In particular, the recursive and modular structure of the algorithms lends itself readily to possible hardware realization.
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    Circuits, systems and signal processing 7 (1988), S. 113-113 
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    Circuits, systems and signal processing 7 (1988), S. 115-118 
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    Circuits, systems and signal processing 7 (1988), S. 173-189 
    ISSN: 1531-5878
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A fixed-size systolic array which can efficiently triangularize arbitrarily large matrices is presented. The array performs orthogonal triangularization by applying Givens' rotations in parallel. For matrices larger than the array, the triangularization is accomplished by emulating a large array with the fixed-size array. The distinguishing features of this array are (1) only one type of cell is used, (2) only unidirectional data flow is required, and (3) the array is rectangular shaped. These properties make it more suitable to emulate arbitrarily large arrays by feedback emulation. The array can also efficiently compute the eigenvalues of arbitrarily large matrices by theQR algorithm, because it can also perform theQR decomposition. In the computation the rotation parameters generated during each stage of theQR decomposition are used in the multiplication before the next stage of decomposition.
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    Circuits, systems and signal processing 7 (1988), S. 213-234 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract On-line signal processing and automatic control applications give rise to numerous examples of computationally intense algorithms. Architectures which are algorithmically specialized and provide massive parallelism are necessary to cope with such computational requirements. Systolic arrays, which feature parallelism, local communications, and VLSI compatability appear to match up well with these computational requirements. This paper summarizes recent research on a general class of nonplanar systolic arrays. These arrays feature closed-loop data flow. The arrays may be switched dynamically to facilitate I/O simplicity and to accommodate iterative calculations without intermediate I/O interdiction. The closed-loop data flows also facilitate restructuring of the array to accommodate specific algorithmic requirements. The potential for multiuser, multialgorithm operation is also enhanced. Matrix operations are used as examples in the development. Algorithms as diversified as the Riccati equation, LU factorization, the Faddeev algorithm, FFT calculation, and controllability Grammians can be implemented on the nonplanar architectures.
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    Circuits, systems and signal processing 7 (1988), S. 275-287 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper two new systolic structures forLU decomposition of an invertible matrix, having 100% and 50% hardware efficiency, are proposed. In comparison, a previously proposed structure forLU decomposition [1] has a hardware efficiency of only 33%. Utilizing one of the proposed systolic structure forLU decomposition, an integrated systolic structure for solving a system of linear equations is also derived. This is unlike other reported systolic structures for solving a system of linear equations, which are obtained by interconnecting heterogeneous subsystems, requiring complicated data realignment. These improvements in the proposed designs have been brought about by giving due consideration to the input/output data flow pattern between various subcomputations.
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    Circuits, systems and signal processing 7 (1988), S. 345-359 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Changing the coefficient set of a recursive digital filter during operation results in a transient signal at the filter output. The amplitude of this transient signal may exceed the amplitude of the output signal before and well after the change of coefficients. This effect is rather disturbing in some applications, such as the processing of audio signals. It is shown how these transients can be minimized without increasing the computational complexity of the filter by the use of a properly chosen set of intermediate coefficients.
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    Circuits, systems and signal processing 7 (1988), S. 409-411 
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    Circuits, systems and signal processing 7 (1988), S. I 
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    Circuits, systems and signal processing 7 (1988), S. 467-479 
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    Notes: Abstract A modeling approach is used in the detection of a random signal in colored noise. The received sequence is modeled as a regressive/autoregressive time series, and the presence or absence of the desired signal is determined through a hypothesis testing procedure. The test is based on the construction of anF-statistic using likelihood functions. The statistic can be easily incorporated into the computation of the probability of a false alarm, such as required in the processing of radar signals. Results based on simulated data and actual radar data are presented.
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    Circuits, systems and signal processing 7 (1988), S. 413-424 
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    Notes: Abstract Recent results for nonconservative dynamical systems involve a variational principle of the Hamilton type. In this approach the velocity of variation and the variation of velocity are not commutative as in the case of mechanics governing conservative dynamical systems. In this paper we adapt the above approach to power systems which include the effects of transfer conductances. For such power systems we show that if certain noncommutative rules (which are consistent with the ones used for the variation of velocities in nonconservative dynamical systems) are used, then it is possible to employ a variational principle of the Hamilton type to derive the classical model for power systems. Numerous simulations of specific postfault multimachine power systems have verified that the above noncommutative rules are indeed satisfied for the types of power systems which we consider. The present results give additional understanding for the types of energy functions that have recently been used in transient stability studies of power systems. In these works, several attributes of energy functions have been ascertained by means of simulations and heuristic reasoning, rather than analysis (e.g., path-dependent terms of energy functions have been approximated by making linear trajectory assumptions).
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    Circuits, systems and signal processing 7 (1988), S. I 
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    Circuits, systems and signal processing 7 (1988), S. 511-511 
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    Circuits, systems and signal processing 7 (1988), S. 21-55 
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    Notes: Abstract This paper depicts the connection between algorithms for the factorization of covariance matrices, a basic operation in linear estimation, and whitening or modeling filters. General algorithms for arbitrary covariances are presented and related to the four fundamental types of cascade filters: feed-forward and feed-back tapped delay line or ladder filter. Systolic implementations of the algorithms and realizations of the associated filters illustrate the correspondence between algorithms and filters. Finally, fast algorithms for special covariances are introduced through two important examples: constant-parameter tapped delay line and ladder filter.
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    Circuits, systems and signal processing 7 (1988), S. 57-78 
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    Notes: Abstract This paper introduces a new nonlinear filter that is used for adaptive noise canceling. The derivation and convergence properties of the filter are presented. The performance, as measured by the root mean square error between the signal and its estimate, is compared with that of the commonly used least mean square (LMS) algorithm. It is shown, through simulation, that the proposed nonlinear noise canceler has, on the average, better performance than the LMS canceler. The proposed adaptive noise canceler is based on the Pontryagin minimum principle and the method of invariant imbedding. The computational time for the proposed method is about 10% of that of the LMS, in the studied cases, which is a substantial improvement.
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    Circuits, systems and signal processing 7 (1988), S. 79-94 
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    Notes: Abstract VLSI systolic and wavefront array processors' architectures for the block implementation of infinite impulse response digital filters with very high sample rates are presented. The proposed systolic array processor achieves the maximum possible throughput rate and requires only local data transfers. The asynchronous wavefront array processor operates at the same maximum throughput rate and, moreover, it is characterized by a substantial reduced latency. The throughput rate of the proposed array processor structures is a linear function of the block lengthL and theoretically it may be arbitrary high; however, it is limited only by a number of practical implications.
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    Circuits, systems and signal processing 7 (1988), S. I 
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    Circuits, systems and signal processing 7 (1988), S. 95-109 
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    Notes: Abstract The main problems that are the major concern in network testing are fault detection, fault location, and fault prediction. In this paper a multiple-fault-prediction algorithm is proposed for analog circuits with inaccessible nodes. The components in the circuits may be nominals or may be deviated from the nominals within a prescribed tolerance. In the proposed prediction algorithm, the component values are evaluated according to the consecutive voltage measurements that are continuously monitored at the accessible test points at each periodic maintenance. The component values are used to locate the faulty components and/or to predict the components that are about to fail.
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    Circuits, systems and signal processing 7 (1988), S. 119-149 
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    Notes: Abstract In this paper we investigate systolic processing for problems formulated in dynamic programming. These problems are classified as monadic-serial, polyadic-serial, monadic-nonserial, and polyadic-nonserial. Problems in serial formulations can be implemented easily in systolic arrays; however, nonserial problems may have to be transformed into a serial one before an efficient implementation can be found. monadic-serial dynamic programming problem can be solved as the search of an optimal path in a multistage graph and can be computed as a string of matrix multiplications. Three efficient systolic-array designs are presented. A polyadic-serial dynamic programming problem can be solved by either a divide- and-conquer algorithm or the search of optimal solutions in a serial AND/OR-graph. We have evaluated the asymptotically optimal architecture for divide- and-conquer algorithms and have developed efficient methods of mapping a regular AND/OR-graph into systolic arrays. Cases are studied for transforming a problem in a nonserial formulation into a serial one.
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    Circuits, systems and signal processing 7 (1988), S. 151-172 
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    Notes: Abstract A prototype filter design is reviewed to underscore the computational problems arising in such designs. A purely systolic-array architecture is presented. This array provides the computational support necessary for filter design. Due to a simple and novel data steering technique the array is capable of carrying out a number of important matrix operations such as factorization, inversion of factors, and matrix-matrix multiplication. Another interesting attribute is the array's ability to maximally overlap computations of multiphase algorithms. In this study we demonstrate the execution of a dense matrix factorization phase and a factor inversion phase on the array with no need for intraphase or interphase I/O. We show that these phases (which are the backbone of an optimal filtering algorithm) are completed in the optimal count of aboutn time units. The array employs 2n n−n simple processing elements (PEs) that are active every other time unit. It is shown that the functions of two adjacent PEs can be merged and assigned to a single PE thus maximizing PE utilization. A possible design of a “merged” PE is given.
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    Circuits, systems and signal processing 7 (1988), S. 191-211 
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    Notes: Abstract Parallel algorithms for solving geometric problems on two array processor models—the mesh-connected computer (MCC) and a two-dimensional systolic array—are presented. We illustrate a recursive divide- and-conquer paradigm for MCC algorithms by presenting a time-optimal solution for the problem of finding thenearest neighbors of a set of planar points represented by their Cartesian coordinates. The algorithm executes on a√n×√n MCC, and requires an optimalO(√n) time. An algorithm for constructing theconvex hull of a set of planar points and anupdate algorithm for thedisk placement problem on ann 2/3×n 2/3 two-dimensional systolic array are presented. Both these algorithms requireO(n 2/3) time steps. The advantage of the systolic solutions lies in their suitability for direct hardware implementation.
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    Circuits, systems and signal processing 7 (1988), S. 235-252 
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    Notes: Abstract In this paper we show how systolic/wavefront arrays can be automatically designed and partitioned to solve problems of arbitrary size. Buffer memory and control of a resulting array is regular and simple, and is generated automatically. Also, the throughput of the array is matched with the I/O speed of the host to which it is to be attached. The approach strongly relies upon classical concepts in signal processing, such as signal flow graphs and state transition functional behavior. Some illustrative examples are included.
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    Circuits, systems and signal processing 7 (1988), S. I 
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    Circuits, systems and signal processing 7 (1988), S. 253-273 
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    Notes: Abstract In this paper we introduce a class of efficient architectures for adaptive quadratic digital filters. These architectures are based on the LMS algorithm and use the rank compressed lower-upper (LU) triangular deomposition method. These architectures exhibit high parallelism as well as great modularity and regularity. We also consider affiliated VLSI array processing structures and compare these in terms of hardware cost and data throughput delay. For comparison purposes, the distributed arithmetic structures of adaptive quadratic filters are also included in the paper. Finally, the convergence performance of the adaptive quadratic filters is tested via benchmark simulation examples.
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    Circuits, systems and signal processing 7 (1988), S. 291-325 
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    Notes: Abstract A new procedure is proposed for ARMA modeling of fourth-order cumulants and trispectrum estimation of non-Gaussian stationary random processes. The new procedure is applied to the identification of nonminimum phase systems for both phase and magnitude response estimation. It is demonstrated by means of comprehensive simulation examples that the ARMA approach exhibits improved performance over conventional trispectrum methods. ARMA model order selection criteria based on fourth-order cumulants are presented and their performance evaluated. The computational complexity of the ARMA and conventional trispectrum methods is also examined. The new procedure does not require knowledge of the non-Gaussian distribution.
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    Circuits, systems and signal processing 7 (1988), S. 327-343 
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    Notes: Abstract This paper deals with the problem of adaptive beamforming in the presence of fully coherent (correlated) noise sources. Two different techniques are developed for minimizing the effects of coherent interference. The first method employs spatial interpolation of the array aperture, followed by spatial smoothing in order to decorrelate the desired signal and the interference. The second technique is based on a simple algebraic transformation for restoring the rank of the array signal correlation matrix, which is normally rank deficient in such situations. This technique is shown to work for nonuniform adaptive arrays as well. Extensive computer simulation results are presented to illustrate the effectiveness of the proposed techniques.
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    Circuits, systems and signal processing 7 (1988), S. 361-380 
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    Notes: Abstract In this paper the notions of transmission zero, invariant zero, and structural zero (that is the geometric notion of zero) are extended to linear periodic discrete-time systems, as well as the notion of pole. Their meaning is clarified and their relationships stressed, thus extending the time-invariant theory. In particular, the invariant zeros and the structural zeros are shown to coincide, together with their multiplicities, and the former are shown to be independent of a linear state feedback. Moreover, the nonzero transmission zeros, the nonzero invariant zeros, and the nonzero poles are shown to be independent of time, together with their multiplicities. Some of these results are obtained with the help of the notions of reachability subspace and inner controllable subspace, which constitute a further development of the geometric theory for this class of systems.
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    Circuits, systems and signal processing 7 (1988), S. 411-411 
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    Circuits, systems and signal processing 7 (1988), S. 381-408 
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    Notes: Abstract We consider the problem of optimal filtering of a scalar diffusion process measured by a monotone nonlinear sensor in a low-noise channel. The specific sensors considered are of the formh n(x)=¦x¦n sgn(x). This case represents a wide class of sensors with a critical inflection point, since it is the leading term in Taylor's expansion of the measurement function in the critical region. We give for the first time a formal asymptotic approximation of the conditional and of the mean square estimation errors of the optimal filter as interpolation formulas. We also construct an asymptotic approximation to the optimal filter and compare its performance with that of a constant gain filter.
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    Bulletin of mathematical biology 50 (1988), S. 345-349 
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    Notes: Abstract A simple scaling (semigroup) property is manifest in the functional form of the effective logistic rate for the increase in the HIV seropositive fraction in the San Francisco (City Clinic) cohort. Witht i=4.5 years, this scaling property—r→λ-2r undert→[λt+(λ−1)t i] for all parameter values λ≧1—encapsulates the effects of relevant biological and sociological changes in the key epidemiological variables during the 8-year seropositive rise period, 1978–1985 inclusive.
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    Bulletin of mathematical biology 50 (1988), S. 367-378 
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    Notes: Abstract Using plausible assumptions a description of the distribution of externally added low molecular weight solutes in individual subcellular regions of biosystems is reduced to a compartmental system of specific structure having, in general, only numerical solutions. Frequently occurring application of biologically active substances in low doses, however, elicits the conditions (i.e. undirectional membrane transport involving accumulation, instantaneous and linear binding to macromolecules and metabolism obeying first order kinetics) that enable one to solve the system explicitly. Equations have been derived, describing the time course of drug concentration in any subcellular phase of arbitrary biosystem having membranes of similar composition, including tissues with a cellular structure (degenerate case). Accuracy of the description is tested on the relationship between physicochemical and biological properties of drugs, bioactivity being used to monitor the concentration in the receptor region.
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    Bulletin of mathematical biology 50 (1988), S. 411-419 
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    Bulletin of mathematical biology 50 (1988), S. 547-558 
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    Notes: Abstract The influence of unstirred layers in osmotic experiments designed to measure the osmotic permeability of a tubule wall is considered. Results are given in the form of a set of graphs whose axes are closely related to observed and known experimental parameters. These enable osmotic permeability values to be obtained which are closer to the true values.
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    Bulletin of mathematical biology 50 (1988), S. 559-565 
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    Notes: Abstract In our previous paper we have given a neuroglia modulated neuronal network model which may display chaotic behaviours under certain parametric values. This work is an attempt to correlate the functions of conscious human brains with the chaotic states shown by the EEG patterns under different physiological conditions. Some of the difficulties and precautions of this kind of work are discussed.
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    Bulletin of mathematical biology 50 (1988), S. 577-577 
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    Bulletin of mathematical biology 50 (1988), S. 579-593 
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    Notes: Abstract By estimating relevant time scales, a simple new condition can be found that ensures the validity of the steady state assumption for a standard enzyme-substrate reaction. The generality of the approach is demonstrated by applying it to the determination of validity criteria for the steady state assumption applied to an enzyme-substrate-inhibitor system.
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    Notes: Abstract A simplified one-dimensional model system was used to test the possibility that physically realistic parameters would lead to the prediction of microscopic heterogeneity of radioligand distribution in the brain and that microscopic heterogeneity of radioligand and neuroreceptor distribution could influence the macroscopically observedin vivo kinetics. The model was represented mathematically by a partial differential equation which is similar to the heat diffusion equation, but with special boundary conditions. The equation was solved analytically under the condition of negligible receptor occupancy by inversion of the Laplace transform and in the more general case of arbitrary receptor occupancy by cubic spline approximation. In simulations with physically reasonable values for rate constants and parameters, we find that significant radioligand gradients can occur. Thus, the level of radioligand in the immediate vicinity of the receptor may be substantially different from the average level in a macroscopically measured region of interest. In order to analyze the simulated data, we derived a rigorous steady-state solution, including both a statement of necessary and sufficient conditions for the validity of the steady-state approximation as well as a demonstration of the proper technique for assessing the consistency of the derived parameter with the requirements of the approximation. The radioligand heterogeneity leads to significant errors in the parameters estimated in the steady-state kinetic analysis. In particular, the pseudo first-order rate constant for radioligand-neuroreceptor association, which is often used as a measure of the total amount of neuroreceptor, is underestimated. The first-order rate constant for radioligand-neuroreceptor dissociation is also underestimated. These effects can partially account for the experimentally-observed discrepancy betweenin vivo andin vitro estimates of these kinetic parameters.
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    Bulletin of mathematical biology 50 (1988), S. 595-634 
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    Notes: Abstract Many developing systems obey the principle of continuity: a morphogenetic field, when perturbed, tends to restore the normal local pattern of structures in its organ district. We have investigated physical field theories for a morphogenetic field, seeking constraints which would make a field theory produce the principle of continuity. We assume that during embryonic (ontogenetic) development a leg develops a pattern of positional values and a length which extremize a time-independent functional—the integral, over the length of the leg, of a function of positional values and position. For a single state variable which represents positional value, if a unique extremizing solution for the ontogenetically generated pattern and the length exists, and if no position-dependent functions other than the state variable appear in the integrand, then the principle of continuity is valid: in any regenerated leg the state variable is continuous and each region is locally identical to a region of the ontogenetically generated leg. This proposition is applied to three simple examples. For an exponential gradient and a Jacobi elliptic function there is a set of parameter values and boundary values for which a functional is minimized and the ontogenetically generated leg has an optimal length. Thus a leg which meets these constraints will obey the principle of continuity. However, a functional which when extremized gives a sinusoidal pattern does not in general provide a unique extremal length. Mathematical conditions are discussed under which an ontogenetically generated limb or a regenerated limb represents an asymptotically stable steady state. For a specific model of the transient dynamics in the exponential gradient case, the steady state gradient is asymptotically stable.
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    Bulletin of mathematical biology 50 (1988), S. 661-679 
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    Notes: Abstract Rhythmic “circa-second” contrations of larvae of the hornetVespa orientalis, believed to serve as hunger signals, were studied. A considerable degree of coordination among individual larvae, both in frequency and phase of these contractions, has been observed. The oscillations of singly isolated larvae are of short duration, non-constant, with increasing intervals in between and there is a substantial variability in the patterns shown by different larvae. In contrast, the association of two or more larvae leads to enhancement of their periodic behaviour and to (partial) entrainment. Communication among larvae may perhaps be mediated by the sound pulses (“scratching” noises) which are generated by these contractions. We have subjected individual and grouped larvae to external sound pulses and were able to demonstrate: (a) enhancement of rhythmic activity; (b) phase resetting; (c) entrainment to an external oscillator within a range of frequencies; (d) the existence of a subharmonic mode of entrainment. We propose a simple phenomenologic model to account for these larvae responses. Our model assumes the existence of an “energy” variable which declines with time but is upgraded, in a phase-dependent way, by external stimuli.
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    Bulletin of mathematical biology 50 (1988), S. i 
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    Bulletin of mathematical biology 50 (1988), S. 1-17 
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    Notes: Abstract Multiple solutions of a model describing immune surveillance against cancer are studied. The model was proposed by R. Lefever and co-workers. A limit cycle solution and two kinds of wave front solutions are worked out by means of a perturbation method. The problem of nucleation concerning this model is studied by a singular-perturbation technique. In addition, the pulse wave solution is also found by numerical simulations.
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    Bulletin of mathematical biology 50 (1988), S. 19-34 
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    Notes: Abstract It is productive to view the suture-lines on fossil cephalopod shells as simple Fraunhoeffer diffraction patterns which can be inverted, by elementary Fourier Transformation, to provide a clear holographic image of the soft body-mass that produced them. As fleshy body organs are rarely ever preserved in ancient fossils it is particularly valuable to be able to deduce soft anatomy from conspicuous and usually well-preserved shell markings. Preliminary studies reported in this paper supply insight into the ontogeny and phylogeny of ancient cephalopods.
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    Bulletin of mathematical biology 50 (1988), S. 43-66 
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    Notes: Abstract This paper is concerned with a population of neurons with dense random interconnections, in which the stimulations between neurons are independent of their distance apart. This study is conducted from the viewpoint of the General System Theory. Proposed and used for the first time in studies on the above subject is a new concept referred to as the ‘historical report’ of the mentioned population. It will be shown that the population exhibits cyclic modes of behaviour which are dependent on its structure and historical report and which in the phase space correspond to cycles of hysteresis. A simple model in discrete time is developed and demonstrates, by the help of a computer study, the existence of the cycles of hysteresis.
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    Bulletin of mathematical biology 50 (1988), S. 77-92 
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    Notes: Abstract A class of non-linear similarity functionss 1 has been proposed for comparing subalignments of biological sequences. The distribution of maximals 1-similarities is well approximated by the extreme value distribution. The significance levels ofs 1 are studied for a variety of nucleotide frequency distributions as well as for several matrices of amino acid substitution costs. Also, the significance levels ofs 1 are explored for comparing three biological sequences. Several previously described subalignments of bovine proenkephalin and porcine prodynorphin are shown to be highly significant.
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 193-207 
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    Bulletin of mathematical biology 50 (1988), S. 289-311 
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    Notes: Abstract A mathematical model of capillary-tissue exchange is presented and the method of solution of the resulting equations is described. The model includes the mutual interaction of fluid movement across the capillary wall and the convection and diffusion of a number of solutes. A variety of solutions for situations of physiological interest are obtained and discussed.
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    Bulletin of mathematical biology 50 (1988), S. 255-288 
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    Notes: Abstract A theory is presented for appearance of periodic band patterns of ion concentration and electric potential associated with electric current surrounding a unicellular or multicellular system of a cylindrical shape. A flux continuity at the membrane (or the surface) is reduced to a nonlinear equation expressing passive and active fluxes across the membrane and intracellular diffusion flux. It is shown that, when an external parameter is varied from the sub-critical region, i.e. the homogeneous flux state, a symmetry breaking along a longitudinal axis usually appears prior to the one along a circumferential direction. The spectrum analysis shows that the correlation length is longer in the longitudinal direction. Growth of the band pattern from a patch-shaped pattern is demonstrated by the use of numerical calculations of proton concentration on the two-dimensional space of cylindrical surface. An experimental example of formative process of H+ banding is given for the internodal cell ofChara. It is shown that small patches on the surface decline or are sometimes gathered to the band surrounding the circle. The resulting pattern is suggested as a kind of dissipative structure appearing far from equilibrium.
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    Bulletin of mathematical biology 50 (1988), S. 227-253 
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    Notes: Abstract Many theoretical studies in biological and physical sciences consider the dynamical behavior of ann-dimensional ordinary differential equation that contains a large number of independent parameters. A frequently asked question is, are there permissible parameter sets that result in periodic or chaotic behavior? The large number of distinct parameters often limits the feasibility of trial and error calculations. The large dimension and nonlinearity of the system make application of analytic methods at best difficult and at worst effectively impossible. It is shown here that a computational search for parameter-dependent transitions of attractor topology can be effected by constrained optimization of quantitative measures of dynamical behavior (Hurwitz polynomials, Floquet coefficients, Lyapunov exponents and correlation dimension). As an example, we examine a three-dimensional nonlinear ordinary differential equation containing seven parameters that was constructed by Goldbeter and Segel to model periodic synthesis of cyclic AMP inDictyostelium. A search for bifurcations to periodic solutions is made by minimizing Hurwitz coefficients subject to parameter constraints. By comparing four optimization algorithms, the defects and advantages of the procedure are identified. It is also argued that it may be possible to use this characterization of dynamics to construct optimal responses to dynamical diseases (those disorders that result from parameter-dependent bifurcations in physiological control systems).
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    Bulletin of mathematical biology 50 (1988), S. 351-366 
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    Notes: Abstract Survival analyses of populations are developed in dicrete growth processes. Persistence and extinction attributes of age-structured discrete population models are explored on both a finite and infinite time horizon. Conditions for persistence and extinction are found. Decompositions of the initial population size axes into intervals where populations are persistent at timeN and intervals leading to extinction at timen, wheren≤N, are given for two age class discrete population models.
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    Bulletin of mathematical biology 50 (1988), S. 329-344 
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    Notes: Abstract A simple mathematical model depicting blood flow in the capillary is developed with an emphasis on the permeability property of the blood vessel based on Starling's hypothesis. In this study the effect of inertia has been neglected in comparison with the viscosity on the basis of the smallness of the Reynolds number of the flow in the capillary. The capillary blood vessel is approximated by a circular cylindrical tube with a permeable wall. The blood is represented by a couple stress fluid. With such an ideal model the velocity and pressure fields are determined. It is shown that an increase in the couple stress parameter increases the resistance to the flow and thereby decreases the volume rate flow. A comparison of the results with those of the Newtonian case has also been made.
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    Bulletin of mathematical biology 50 (1988), S. 421-422 
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    Bulletin of mathematical biology 50 (1988), S. I 
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    Bulletin of mathematical biology 50 (1988), S. 445-464 
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    Notes: Abstract Adaptation is viewed as a tendency maximizing the Shannon entropy of an ecosystem, where the ecosystem is considered as two interacting subsystems, namely, the biota and its environment. We derive theadapted structures starting from three fundamental hypotheses and we apply this result to an ecological topic: the cryptic and aposematic behaviour.
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    Bulletin of mathematical biology 50 (1988), S. 465-491 
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    Notes: Abstract The behavior of a model that generalizes the Lotka-Volterra problem into three dimensions is presented. The results show the analytic derivation of stability diagrams that describe the system's qualitative features. In particular, we show that for a certain value of the bifurcation parameter the system instantly jumps out of a steady state solution into a chaotic solution that portrays a fractal torus in the three-dimensional phase space. This scenario, is referred to as the explosive route to chaos and is attributed to the non-transversal saddle connection type bifurcation. The stability diagrams also present a region in which the Hopf type bifurcation leads to periodic and chaotic solutions. In addition, the bifurcation diagrams reveal a qualitative similarity to the data obtained in the Texas and Bordeaux experiments on the Belousov-Zhabotinskii chemical reaction. The paper is concluded by showing that the model can be useful for representing dynamics associated with biological and chemical phenomena.
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    Bulletin of mathematical biology 50 (1988), S. 503-515 
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    Notes: Abstract Traditional population models describe changes in population size as a function of changes in the resources. Such first-order models cannot describe certain properties of population dynamics. General models with delays can account for all the observed dynamic complexities but are judged overgeneralized. It is proposed that the simplest model of intermediate complexity that explains such dynamic properties is a second-order model, which describes population dynamics as a function of a physiological variable, the dynamics of which in turn depends on resources. Data on accelerated decline of populations in the absence of food from experiments with brown and green hydra as well as literature data support the arguments.
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    Circuits, systems and signal processing 7 (1988), S. 459-466 
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    Notes: Abstract A generalized Leverrier's algorithm is developed for the computation of the transfer function matrix of a singular two-dimensional discrete-time system. The algorithm is a recursion in terms of the original system matrices, and does not require the inversion of a polynomial matrix.
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    Circuits, systems and signal processing 7 (1988), S. 427-457 
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    Notes: Abstract In this paper a new method to image restoration problems is proposed. The main result is the definition of an image model which does not require knowledgea priori of the image autocorrelation function or the use of identification estimation algorithms. The basic hypothesis is that the image can be modeled as an ensemble of two-dimensional differentiable surfaces. In this case the signal and its partial derivatives with respect to the spatial coordinates can be assumed to be the state vector and an image state space representation is directly obtained. A semicausal dependence model is adopted, it is embedded in a strip recursive scheme suitable to the Kalman filter application. Numerical results, concerning three different kinds of images, show high performances of the algorithm.
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    Circuits, systems and signal processing 7 (1988), S. 481-510 
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    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper describes a method of fault diagnosis for large interconnected circuits in which the number of faults is limited to, say,n f where it is possible thatn f exceeds the number of output measurements,n o. The problem and its solution are formulated in the context of a frequency domain tableau based on the component connection model of a circuit/system. The paper describes Jacobian tests for diagnosability whenn f≥n o and states a full parameter diagnosability test as a corollary to the main theorem. An algorithm is developed for the identification of faulty parameters in this limited fault case. Finally, examples, including a 26-parameter video-amplifier circuit, illustrating the technique are given.
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  • 79
    ISSN: 1522-9602
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    Topics: Biology , Mathematics
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    Bulletin of mathematical biology 50 (1988), S. I 
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  • 81
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    Bulletin of mathematical biology 50 (1988), S. 313-328 
    ISSN: 1522-9602
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  • 82
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    Bulletin of mathematical biology 50 (1988), S. I 
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  • 83
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 1-8 
    ISSN: 1476-5535
    Keywords: Penicillium roqueforti ; Methyl ketone ; Aroma ; Buckwheat ; Volatile loss
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The synthesis of 2-heptanone from the sodium salt of octanoic acid by spores of five strains ofPenicillium roqueforti was studied. The strains showed a high disparity in kinetic behavior. The one selected, which was originally isolated from blue cheese, had a good resistance to substrate inhibition along with a good apparent biotransformation yield (close to 60%). An activator was needed in the incubation medium. The loss of activity of aging spores was reduced by the activator compounds; ethanol exhibited the highest efficiency. When spores were produced on buckwheat seeds with a solid state fermentation technique, the medium itself was an activator source. When the biotransformation reaction was carried out in a stirred aerated fermentor, the volatile loss by air-stream stripping had to be taken into account. No ketone metabolism occurred with the strain used.
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  • 84
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 15-19 
    ISSN: 1476-5535
    Keywords: Cheese whey ; Clostridium beijerinckii ; Bacillus cereus ; Fermentation
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Fermentation of cheese whey to produce butanol and butyric acid was carried out using a mixed culture ofClostridium beijerinkii andBacillus cereus. Fermentation selectivities were studied by controlling the pH of the system. Controlled pH values higher than 6.5 as well as those below 5.0 were not conducive to butanol production. Maximum product formation was obtained by controlling the pH at 5.5. When compared with the results obtained using the pure culture ofC. beijerinckii, a higher butanol concentration was obtained in the mixed culture without sacrificing the level of butyric acid formed.
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  • 85
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 57-59 
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    Keywords: Thienamycin ; Methionine interference ; Streptomyces cattleya
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    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Methionine interference in the formation of thienamycin byStreptomyces cattleya is due, to a major extent, to inhibition of enzyme activity.
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  • 86
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 61-71 
    ISSN: 1476-5535
    Keywords: Casein ; Solubility profile ; Primary structure ; Posttranslational modification ; Protein functionality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Molecular biology holds the promise of new tools for the food industry which include proteins with tailor-made functionality. Without a fundamental knowledge of the molecular bases of these properties, implementation will be strictly empirical. For example, the phenomena of salt-induced precipitation of proteins (salting-out) and their resolubilization (salting-in) has heretofore been discussed only qualitatively. A quantitative method, using Wyman's theory of thermodynamic linkage, has been developed and tested on the calcium-induced solubility profiles of the major milk proteins, the caseins. Salting-out was described by a salt-binding constant,k 1, andn, the number of moles of salt bound; salting-in was described by the corresponding termsk 2 andm. The magnitude of these parameters indicated involvement of protein phosphate groups in binding and precipitation, but enzymatic dephosphorylation showed significant increases ink 1 andk 2 indicating involvement of carboxylate groups as well. Studies on two genetic variants of αs1-casein indicated the importance of a hydrophobically stabilized intramolecular ion pair in the functionality of the protein. These studies have led to a fuller understanding of the molecular basis for the solubility behavior of caseins and have laid the groundwork for future computer simulation of food protein functionality.
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  • 87
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 89-103 
    ISSN: 1476-5535
    Keywords: Food protein ; Milk protein ; Egg protein ; Protein structure, tertiary ; Small-angle scattering ; β-Lactoglobulin ; α-Lactalbumin ; Lysozyme ; Ribonuclease ; Riboflavin-binding protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary With current emphasis in bioengineering on developing new and better structure-function relationships for proteins (e.g., the need for predictability of expected properties prior to cloning), practical and reliable methodology for providing characterization of appropriate features has become of increasing importance. The most potent and detailed technique, X-ray crystallography, has severe limitations: it is so demanding and time-consuming that X-ray coordinates are frequently unavailable for materials of interest; its data relate to static and essentially unhydrated structures, whereas proteins exhibit a variety of dynamic features and function in an aqueous environment; and many proteins of technological importance may never be crystallized. Small-angle X-ray scattering, however, is particularly suitable as a methodology that can provide a substantial number of significant geometric parameters consistent with crystallographic results, that can readily show tertiary structural changes occurring under varying conditions, and that can deal with solutions and gels. Results are presented here from small-angle X-ray scattering investigations of the apo and holo forms of chicken egg-white riboflavin-binding protein, chicken egg-white lysozyme, bovine milk-whey α-lactalbumin and β-lactoglobulin, and bovine ribonuclease. We utilize these observations to compare tertiary structures of these proteins as well as conformational changes in these structures, and to provide a basis for discussion of their physical and biological significance.
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  • 88
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 127-137 
    ISSN: 1476-5535
    Keywords: Serine protease ; Limited proteolysis ; Biomacromolecular architecture ; Genetic engineering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary We have been developing computational approaches to increase our ability to analyze the growing body of three-dimensional structural data with applications centered on the serine proteases and their natural inhibitors and substrates. It is essential that these approaches emphasize the comparison of these macromolecules at the separate levels of secondary, tertiary and quaternary structure. We assume in our analysis that in functionally related macromolecules (i.e., a family of evolutionarily related enzymes), regions of structural and/or physicochemical similarity will exhibit functional similarity; regions that are different in structure and/or physicochemical properties will function differently and, therefore, be the source of observed specificity. It is the intent of our research to encapsulate such ‘knowledge’ in a form which is capable of observing patterns which may serve as generalizable rules for macrostructural analysis (Liebman, M.N. 1986. Enzyme 36: 150–163), and to serve as the essential ‘tools’ for the rational design of modified serine proteases and/or their natural inhibitors by the methods available through genetic engineering.
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  • 89
    ISSN: 1476-5535
    Keywords: Catharanthus roseus ; Sterol ester ; Lipid ; Indole alkaloid ; Acetyl coenzyme A ; Tryptamine ; Tryptophan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A cell line, NA13-2, was selected as a rapidly growing colony of protoplasts from a UV(254 nm)-fluorescent cell line, NA13-1, which originated from a tryptamine-resistant strain ofCatharanthus roseus NA13. Cell line NA13-2 lost the capability to produce indole alkaloids. Tryptophan fed to these cells was converted toN b-acetyltryptamine as the major product. The free acetyl coenzyme A content of NA13-2 cells was 50% higher than in the mother cells. The total lipid content of the NA13-2 cells was 2.5-fold that in the NA13 cells. In spite of the similarity in the fatty acid content to that of the mother cell line NA13, the total lipid extract of NA13-2 cells appeared as a wax instead of an oil, resulting from the presence of sterol esters.
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  • 90
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 311-320 
    ISSN: 1476-5535
    Keywords: Recombination ; Protoplast fusion ; Streptomyces avermitilis ; Avermectin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The power of protoplast fusion as a generally applicable method for obtaining genetic recombination is demonstrated by the recombination of genes involved in avermectin biosynthesis. A backcross ofStreptomyces avermitilis strain MA6202, an improved mutant that had lost the ability to carry out the methylation of the C-5 hydroxyl of the avermectin molecule, with the original soil isolate MA4680 resulted in the recovery of at least one unambiguous recombinant class despite the instability of rifampicin resistance, one of two markers initially used for recombinant selection. Such intrinsic instability is frequently encountered in streptomycete genetics, and this result delineates the utility of protoplast fusion as a genetic tool. Other difficulties addressed include recovery of complementary recombinant classes, differences in recombination frequency due to colony density on regeneration medium, and alteration in plating efficiency on diagnostic media following protoplasting and regeneration. The results of a cross between a nicotinamide auxotroph MRG1003 and a lysine auxotroph MRG 1004 are included to aid in the elucidation of these problems as well as to support the finding of homologous recombination inS. avermitilis.
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  • 91
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 179-194 
    ISSN: 1476-5535
    Keywords: Aquifer ; Biodegradation, anaerobic ; Pollutant ; Groundwater ; Methanogenesis ; Sulfate-reduction ; Ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Anaerobic microbial communities sampled from either a methanogenic or sulfate-reducing aquifer site have been tested for their ability to degrade a variety of groundwater pollutants, including halogenated aromatic compounds, simple alkyl phenols and tetrachloroethylene. The haloaromatic chemicals were biodegraded in methanogenic incubations but not under sulfate-reducing conditions. The primary degradative event was typically the reductive removal of the aryl halides. Complete dehalogenation of the aromatic moiety was required before substrate mineralization was observed. The lack of dehalogenation activity in sulfatereducing incubations was due, at least in part, to the high levels of sulfate rather than a lack of metabolic potential. In contrast, the degradation of cresol isomers occurred in both types of incubations but proved faster under sulfate-reducing conditions. The requisite microorganisms were enriched and the degradation pathway forp-cresol under the latter conditions involved the anaerobic oxidation of the aryl methyl group. Tetrachloroethylene was also degraded by reductive dehalogenation but under both incubation conditions. The initial conversion of this substrate to trichloroethylene was generally faster under methanogenic conditions. However, the transformation pathway slowed when dichloroethylene was produced and only trace concentrations of vinyl chloride were detected. These results illustrate that pollutant compounds can be biodegraded under anoxic conditions and a knowledge of the predominant ecological conditions is essential for accurate predictions of the transport and fate of such materials in aquifers.
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  • 92
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 231-239 
    ISSN: 1476-5535
    Keywords: Aureobasidium pullulans ; Color variant ; Cornstarch ; Pullulan ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Naturally occurring ‘color variant’ strains ofAureobasidium pullulans are distinguished from typical strains by their brilliant pigmentation, overproduction of secreted enzymes (xylanase), and low DNA relatedness. Color variants have not previously been examined for pullulan secretion. Among five independently isolated color variants, strains NRRL Y-12,974 and YB-4026 made the greatest amounts of pullulan from cornstarch, with conversion efficiencies of about 10%. Neither color variant nor typical strains made significant amounts of pullulan from the unconventional lactose or xylan substrates. Pullulan yields were inversely correlated with biomass production. Pullulan production thus appears to be a variable characteristic of both color variant and typically pigmented strains ofA. pullulans, regulated by specific inducers during growth limitation.
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  • 93
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 253-257 
    ISSN: 1476-5535
    Keywords: Granulation ; Lactic acid bacteria ; Culture ; Coating ; Microencapsulation ; Stabilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary A method to produce viable and stabile dry microorganisms for food and agricultural purposes was developed. Spray-dried, freeze-dried or liquid culture concentrates of lactic acid-producing bacteria were mixed with various bulking agents to form a homogeneous wet granulation having a water content of 35–60% (w/w). The wet granulation was extruded through a dye onto a spinning plate (350–500 rpm) of a spheronizing device which resulted in the formation of discrete spherical particles. After forming spheres, the aggregate cell particles, both coated and uncoated, were dried to a moisture level of 5–10% using a temperature below the microorganism's optimum growth temperature. The coated and uncoated products were stored at different temperatures and periodically sampled to determine stability. Uncoated cell particles were more stabile at 4°C than at 22°C for 76 days. While both coated (with sodium alginate or carboxymethyl-cellulose) and uncoated particles showed similar stability at 4°C, at higher storage temperatures the applied coating improved the storage stability of the culture particles.
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  • 94
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 273-280 
    ISSN: 1476-5535
    Keywords: Adsorption ; Cellulase ; Cellulose ; Lucerne fiber ; Trichoderma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Protein-extracted lucerne fibers (PELF) had a higher adsorptive capacity forTrichoderma reesei cellulases than a variety of other cellulosic substrates compared on an equal carbohydrate basis. Adsorption at room temperature reached a maximum at about 5 min; desorption was directly proportional to the extent of carbohydrate solubilization. Cellulase binding conformed to a Langmuir isotherm; the maximum cellulasebinding capacity of PELF was 111 filter paper units per g dry weight. About 85% of the cellulase was recovered in the soluble fraction after PELF hydrolysis. Soluble carbohydrates in the hydrolysate inhibited cellulase adsorption to fresh substrate (50% inhibition at a hydrolysate concentration of 7% glucose equivalents). The effect of these carbohydrates on cellulase adsorption was a complex one composed of both enhancing and inhibitory influences. Artificial hydrolysates (known sugars in proportions identical to actual hydrolysates) inhibited adsorption, but glucose, cellobiose and xylose resulted in adsorption enhancement. Acid treatment of the hydrolysate to convert oligosaccharides to monomers increased reducing sugar concentrations and eliminated its capacity for adsorption inhibition.
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 299-304 
    ISSN: 1476-5535
    Keywords: Anaerobe ; Antibiotic resistance ; Irradiation ; Mutation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Based on a dose-survival curve, a radiation dose of 3.99 C/kg was used to induce antibiotic-resistant mutants inBacteroides fragilis. Escherichia coli B/r membrane fragments were employed as a reducing agent. Antibiotic-resistant mutants ofB. fragilis were utilized to study the mechanism by which these organisms become resistant to selected chemotherapeutic agents. Decreased accumulation of tetracycline by resistant mutants ofB. fragilis suggests that the resistance to this antibiotic is associated with the outer membrane permeability. There is a marked difference in the inhibitory action of rifampicin on RNA polymerase activity in rifampicin-sensitive and-resistant strains ofB. fragilis. This enzyme is, therefore, the likely target for inhibition of bacterial growth in this anaerobe by rifampicin.
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  • 96
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 343-350 
    ISSN: 1476-5535
    Keywords: Thermophilic actinomycete ; Actinomycete ; Debranching enzyme ; pullulanolysis ; Saccharification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Thermoactinomyces thalpophilus No. 15 produced an extracellular pullulanase in an aerobic fermentation with soluble starch, salts, and complex nitrogen sources. Acetone fractionation, ion-exchange chromatography, and gel filtration purified the enzyme from cell-free broth 16-fold to an electrophoretically homogeneous state (specific activity, 1352 U/mg protein; yield, 4%). The purified enzyme (estimated MW 79 000) was optimally active at pH 7.0 and 70°C and retained 90% relative activity at 80°C (30 min) in the absence of substrate. The enzyme was activated by Co2+, inhibited by Hg2+, and exhibited enhanced stability in the presence of Ca2+. The enzyme hydrolyzed pullulan (K m 0.32%, w/v) forming maltotriose, and hydrolyzed amylopectin (K m 0.36%, w/v), amylopectin beta-limit dextrin (K m 0.45%, w/v) and glycogen beta-limit dextrin (K m 1.11%, w/v) forming maltotriose and maltose.
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  • 97
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 373-376 
    ISSN: 1476-5535
    Keywords: Agricultural by-product ; Fermentation ; Ammonium lactate ; Probiotic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Deproteinized alfalfa juice is a by-product of the mechanical fractionation of alfalfa to obtain protein. In this work the juice was used as the substrate for the production of ammonium lactate (l-lactic acid) by a strain ofStreptococcus faecium. Batch fermentation with a constant pH of 5.8 gave 27.2 g/l of lactic acid (90% conversion and 1.1 g/l/h productivity) and 6×1012 cells/l after 24 h. Semicontinuous fermentation allowed the conversion of 3-times the volume of deproteinized juice after 44 h, finally giving 29.7 g/l of ammonium lactate (99% conversion and 2.5 g/l/h productivity) and 4–6×1012 cells/l.
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  • 98
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 73-88 
    ISSN: 1476-5535
    Keywords: Spectroscopy, computerized ; IR spectroscopy ; Raman spectroscopy ; Protein structure-function relationship ; Conformation study
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The ability of modern biotechnology to produce new or modified proteins has outpaced current understanding of the relationship between protein structure and protein function. Resolution-enhanced infrared spectroscopy and Raman spectroscopy are excellent non-destructive techniques for investigating the secondary structure of proteins under a wide variety of conditions. The techniques yield rapid, reliable estimates of the proportion of helical structure, β-strands, and turns of proteins in solution, as gels, or as solids. These methodologies can also detect subtle variations in protein conformation that frequently occur upon change of the biomolecular environment. In particular, it is possible to study structural changes which arise from alterations in pH, ionic strength, nature of solvent, and from interactions with other molecules or ions, such as another protein or Ca2+ ions. The first part of this paper will briefly review various important aspects of the techniques. The subsequent part describes application to structural problems of casein and other food proteins.
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 111-117 
    ISSN: 1476-5535
    Keywords: Cladosporium resinae ; Microbody ; Catalase ; Spheroplast ; Hydrocarbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Cells ofCladosporium resinae form greater numbers of microbodies when grown onn-alkanes than when grown on glucose. To facilitate isolation of microbodies, hydrocarbon-grown cells were spheroplasted. Of four spheroplasting agents and five osmotic supports examined, best results were obtained after a 4-h incubation with Novozym 234 plus chitinase and with 0.8 M sorbitol as osmotic support. Equal numbers of spheroplasts were obtained at pH 5.8 and at pH 7.0. Catalase was used as a marker for microbodies and cytochrome-c oxidase as a marker for mitochondria. Urate oxidase, a second marker for microbodies, was not detected in cell extracts. Microbodies were extremely fragile; of eight spheroplast disruption techniques attempted, the best yield of microbodies was obtained using a Teflon homogenizer for 5 min. Microbodies were partially purified by differential and density gradient centrifugation. Best results were obtained with discontinuous Percoll gradients which yielded a fraction enriched in microbodies and one enriched in mitochondria.
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    Journal of industrial microbiology and biotechnology 3 (1988), S. 139-146 
    ISSN: 1476-5535
    Keywords: Biofilm ; Plasticity ; Adherent bacteria ; Elongation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The growth of two strains ofPseudomonas aeruginosa in stirred batch cultures was monitored by optical density, DNA concentration, and acridine orange direct cell count measurements. Growth of adherent bacteria in pure culture was also observed on suspended glass discs by light and scanning electron microscopy. Strain MUCOID produced significant numbers of filamentous cells in broth culture and in the adherent population, while strain PAO 381 did not produce elongated cells. Filamentous growth of MUCOID could be prevented by the addition of 5 × 10−2 M Mg2+. However, the addition of 0.66 mM EDTA caused an increased proportion of the population (〉50%) of MUCOID cells to become filamentous in broth culture. The results are discussed and related to theories regarding bacterial plasticity, and filamentation of normally bacillary cells.
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