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  • 1
    Electronic Resource
    Electronic Resource
    Different biological behavior of AKR lymphoma cells from primary and metastatic tumors (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 404-407 
    Details
    ISSN: 1420-9071
    Keywords: Different malignancy ; primary-metastatic cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary AKR lymphoma cells derived from primary s.c. tumors (PT) and cells from their metastases (MT) were inoculated into recipient mice in order to compare their malignant behavior. A higher malignant potential of MT compared to PT cells was found. The results support the hypothesis that metastasis is a process of selection of cells possessing a potential to metastasize, which preexist in the primary tumor. In the model used, both the selection of ‘variants’ of malignancy and the assay of malignancy were as close as possible to natural tumor progression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02004530
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  • 2
    Electronic Resource
    Electronic Resource
    Development of visual sensitivity in the fly,Sarcophaga bullata (1983)
    Springer
    Cellular and molecular life sciences 39 (1983), S. 1318-1319 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ontogeny of light response in the compound eyes of the fly,Sarcophaga bullata was investigated. Even though the eyes are structurally differentiated before eclosion they become electrophysiologically functional only after eclosion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01990392
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature-jump and voltage-jump experiments at planar lipid membranes support an aggregational (micellar) model of the gramicidin A ion channel (1986)
    Springer
    The journal of membrane biology 89 (1986), S. 23-37 
    Details
    ISSN: 1432-1424
    Keywords: gramicidin A ; ion channel ; lipid membrane ; temperature jump ; voltage jump
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The kinetics of formation and dissociation of channels formed by gramicidin A and two analogues in planar lipid membranes was studied using a laser temperature-jump technique developed earlier [Brock, W., Stark, G., Jordan, P.C. (1981),Biophys. Chem. 13:329–348]. The time course of the electric current was found to agree with a single exponential term plus a linear drift. In case of gramicidin A the relaxation time was identical to that reported for V-jump experiments [Bamberg, E., Läuger, P. (1973),J. Membrane Biol. 11:177–194], which were interpreted on the basis of a dimerization reaction. The same results were obtained for gramicidin A and for chemically dimerized malonyl-bis-desformylgramicidin. It is therefore suggested that the dimerization represents a parallel association of two dimers to a tetramer. There is evidence that the tetramer, contrary to the presently favored dimer hypothesis, is the smallest conductance unit of an active gramicidin channel. An additional V-jump-induced relaxation process of considerably larger time constant is interpreted as a further aggregation of gramicidin dimers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870893
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic definition of a further gene region and identification of at least three different histocompatibility genes in the rat major histocompatibility system (1980)
    Springer
    Immunogenetics 11 (1980), S. 483-490 
    Details
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Two new recombinant haplotypes of the rat major histocompatibility system,RT1, have been detected in [LEW.1A (RT1 a ) ×LEW.1W (RT1 u )] × LEW 1N(RT1 n ) segregating hybrids. Recombinantr3 carries theRTL1. A region (determining classical transplantation antigens) and theRT1.B region (determining strong mixed lymphocyte reactivity and genetic control of antipolypeptide immune responsiveness) of the RT1a parent, bur rejects RT1a skin grafts. Recombinantr4 carries theA andB regions of the RT1u parent, but rejects RT1u skin grafts. The two histocompatibility genes detected are allelic to each other. The relevant locus, designated asH-C, maps to theB-region side of theRT1 system and appears to mark a thirdRT1 gene region,RT1.C. Availability of haplotypes r3 andr4 allowed the definition of a histocompatibility locus in theB region,H-B. The products ofH-C, H-B and of the previously describedH-A gene vary in antigenic strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01567816
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  • 5
    Electronic Resource
    Electronic Resource
    Sensitivity analysis and optimization for a head movement model (1981)
    Springer
    Biological cybernetics 41 (1981), S. 33-45 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A sixth order nonlinear model for horizontal head rotations in humans is analyzed using an extended parameter sensitivity analysis and a global optimization algorithm. The sensitivity analysis is used in both the direct sense, as a model fitting tool, and in the indirect sense, as a guide to experimental design. Resolution is defined in terms of the sensitivity table, and is used to interpret the sensitivity results. Using sensitivity analyses, the head and eye movement systems are compared and contrasted. Controller signal parameters are the most influential. Their variations and effects on head movement trajectories and accelerations are investigated, and the conclusions are compared with clinical neurological findings. The global optimization algorithm, in addition to automating the fitting of various types of data, is combined with time optimality theory to give theoretical time-optimal inputs to the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01836125
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  • 6
    Electronic Resource
    Electronic Resource
    Muscle models: What is gained and what is lost by varying model complexity (1987)
    Springer
    Biological cybernetics 55 (1987), S. 403-420 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Three structurally different types of models have evolved over the years to describe muscle-joint systems. The first, based on an input-output analysis of a given task, results in a simple second-order differential equation description that is adequate over a certain movement operating range. The second, based on the classic structural model of Hill (1938), results in a higher-order nonlinear model described by ordinary differntial equations. The third, based on an analysis of the biophysical contractile mechanism, results in a complex partial differential equation description. The advantages and disadvantages of each type of model are considered, based on the criteria of identifying the simplest model that can adequately simulate any fundamental type of human movement without modifying model parameters for different tasks. It is shown that an eighth-order Hill-based antagonistic muscle-joint model is able to satisfy these criteria for a given joint if each of the four basic mechanically-significant non-linearities of the system are included in the model. This same model structure has been used successfully for eight different muscle-joint systems, ranging in size from knee flexion-extension to eye rotation — the only difference between the models is in the parameter values. Second-order models are shown to be task-specific special cases of the input-output behavior of the eighth-order model, while the more complex biophysical models are hypothesized to have insignificant advantages and many disadvantages over the Hill-based model during normal human movement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318375
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of head movement trajectories: model and fit to main sequence (1981)
    Springer
    Biological cybernetics 41 (1981), S. 19-32 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract A sixth order nonlinear model for horizontal head rotations in humans is presented and investigated using experimental results on head movement trajectories and neck muscle EMG. The controller signals, structured in accordance with time optimal control theory, are parameterized, and controller signal parameter variations show a dominating influence on different aspects of the head movement trajectory. The model fits the common head acceleration types over a wide range of amplitudes, and also less common (dynamic overshoot) trajectories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01836124
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  • 8
    Electronic Resource
    Electronic Resource
    A model for nonlinear stochastic behavior of the pupil (1982)
    Springer
    Biological cybernetics 45 (1982), S. 13-21 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract In this paper we present new experimental results that show pupillary noise to be multiplicative in a particular fashion with greatest variance in midrange and smaller variance at high and low ranges. This confirms the finding of multiplicative noise by Stanten and Stark (1966), but modifies and extends the relationship they suggested between standard deviation and mean pupil diameter. We propose a parametric model of the iris muscle which not only describes the static characteristics of pupil response to given stimuli, but also explains its random fluctuations in terms of probability density functions. We emphasize the point that the range nonlinearity is not due to decreased gain at the extrema of the pupil range, but is operational over a wide portion of the pupillary behavioral range, hence its name — “expansive range nonlinearity”. We conclude that noise amplitude, which is a function of the pupil diameter, closely parallels the changes in deterministic gain. Thus pupil noise can be simply considered as cross-talk additive Gaussian noise injected into the pupil system at midbrain level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387209
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  • 9
    Electronic Resource
    Electronic Resource
    Multipulse controller signals (1983)
    Springer
    Biological cybernetics 48 (1983), S. 5-8 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract We apply minimum time as an optimality criterion for human saccadic eye movements. This constrains the class of admissable controller signals to those taking only their maximum and minimum values. We then assume set numbers of switchings between maximum and minimum for each extraocular muscle, and explore the space of switching times to find the fastest model-generated trajectory, for each number of switches. We find that controller signals with bursts of antagonist “braking” activity cause much faster movements than do simple pulse-step patterns, and that signals with an extra pulse of agonist innervation produce still faster movements. The slight increase in speed for still more pulses is at the expense of unreasonably short final pulses. The use of the global optimization algorithm confirms and extends our previous study of multipulse control using a parallel processor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336878
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  • 10
    Electronic Resource
    Electronic Resource
    Multipulse controller signals (1983)
    Springer
    Biological cybernetics 48 (1983), S. 1-4 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Although eye movement saccades are stereotyped, repeatable movements, the shape of the neural controller signal innervating the extraocular muscles is a matter of controversy. Different lines of evidence — single motoneuron recordings, electromyograms, and dynamics — lead to different conclusions. Although all agree that the controller is, in outline, a pulse-step of net activity, neither the pulse width nor shape of the trailing edge of the pulse is clear. We use a mathematical model of the eye and two extraocular muscles to link the dynamical data to the electrophysiological evidence. We conjecture a multipulse controller signal, based on the application of an optimality principle to our model. This multi-pulse controller signal raises new possibilities for resolution of the pulse shape ambiguities, and resolves the controversy over pulse width.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336877
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