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At least 199 records · Page 11Linked to original sources
PubMed1996

The need for a new biological model in geratology.

Disease classes have hitherto been based on anatomical pathology and structural lesions belonging to an earlier ecological medical model involving classification. The diseases of ageing now coming to dominate clinical practice evolve across the clinical threshold in middle age parallel to changes occurring in the internal environment. The concept 'multiple pathology' used to describe the plural features of biological changes now requires new intellectual tools by which to understand overlap phenomena. Boolean algebra and Set Theory are proposed as the relevant enabling concepts, and their application to modern clinical practice is discussed.

Aged↗
PubMedDate not supplied

[Evaluation of the possibilities of modeling biological tissues by the Focker-Planck and Gui-Chapman joint system of equations].

When describing the galvanic effect on biological tissues ion diffusion was taken into account in the Focker-Planck model, in the Gui-Chapman model account was taken of bolzman ion distribution while solving Poisson equation. To specify the models joint solution of these equations ought to be carried out. However, the equation system of Focker-Planck and Gui-Chapman proved to be reestimated, and therefore one can speak only about quasisolution as a solution of an incorrectly stated problem.

Diffusion↗
PubMed1982

Optimization of radiation therapy: integral-response of a model biological system.

Several radiotherapy treatment planning criteria have been proposed for dose distribution optimization. Here we present a simple mathematical model of an idealized biological system. From it we have derived an objective function designed to achieve an extremum for that particular plan which minimizes the probabilities of occurrence of unacceptable complications in healthy tissue and of recurrence or spread of disease. The model assumes that an organism is separable into physiologically discrete compartments or organs, each consisting of a set of microscopic functional units with their own dose-response characteristics. In analogy to the integral-dose, we define an integral-response parameter v as a measure of radiation-induced damage; the value of this v may be calculated for any given spatial distribution of dose in a compartment or organ. A Probability of Serious Complications function, PSC(v), then provides an estimate of the likelihood of occurrence of unacceptable complications. Special problems arising with paired organs (kidneys), "series" organs (spinal cord), and the recurrence and spread of disease are addressed. The PSC for the various organs and neoplasia can be combined to form a compound Complication Factor (CF) objective function; the lower the value of the CF, the better the overall plan. Prospects for making the model explicitly time/fractionation dependent, and for incorporating utility theoretic ideas, are discussed.

Humans↗
PubMed2003

Modeling biological invasions into periodically fragmented environments.

Range expansion of a single species in a regularly striped environment is studied by using an extended Fisher model, in which the rates of diffusion and reproduction periodically fluctuate between favorable and unfavorable habitats. The model is analyzed for two initial conditions: the initial population density is concentrated on a straight line or at the origin. For each case, we derive a mathematical formula which characterizes the spatio-temporal pattern of range expansion. When initial distribution starts from a straight line, it evolves to a traveling periodic wave (TPW), whose frontal speed is analytically determinable. When the range starts from the origin, it tends to expand radially at a constant average speed in each direction (ray speed) keeping its frontal envelope in a similar shape. By examining the relation between the ray speed and the TPW speed, we derive the ray speed in a parametric form, from which the envelope of the expanding range can be predicted. Thus we analyze how the pattern and speed of the range expansion are affected by the pattern and scale of fragmentation, and the qualities of favorable and unfavorable habitats. The major results include: (1). The envelope of the expanding range show a variety of patterns, nearly circular, oval-like, spindle-like, depending on parameter values; (2). All these patterns are elongated in the direction of stripes; (3). When the scale of fragmentation is enlarged without changing the relative spatial pattern, the ray speed in any direction increases, i.e., the rate of range expansion increases.

Algorithms↗
PubMed1993

Response of the 23Na-NMR double-quantum filtered signal to changes in Na+ ion concentration in model biological solutions and human erythrocytes.

Double quantum filtered (DQF) 23Na-NMR signals were evaluated as a function of [Na+] at constant temperature in two model systems (bovine serum albumin (BSA) and Ficoll 400) and in human red blood cells (RBCs). In model systems, the ratio of double quantum filtered to single quantum (SQ) signal intensities was independent of [Na+], even over a wide range of Na+/K+ ratios. Varying the DQF preparation time affected only the DQF signal intensity. In contrast, in human red blood cells (RBCs) the shape and phase of the DQF intracellular Na+ signal (Na+in) varied as a function of preparation time. Similar observations in cartilage [Eliav, U., Shinar, H. and Navon, G. (1992) J. Magn. Reson. 28, 223-229] have been attributed to the generation of a second- and a third-rank tensor by the DQF pulse sequence, resulting from Na+ ion ordering. By using a DQF sequence which isolates the second-rank tensor only, this component was found to originate from the intracellular Na+ ion pool in human RBCs, as well as from interactions of Na+ ions with the extracellular face of the plasma membrane. The residual quadrupolar splitting for the signal originating from the former environment was shown to be less than the SQ linewidth, explaining its absence in SQ spectra, and this was confirmed by two-dimensional DQF 23Na-NMR experiments. By isolating the contribution from the third-rank tensor exclusively, the ratio of DQF:SQ signal intensities for Na+in in human RBCs was shown to be constant over a 4-fold change in [Na+in] produced by addition of an ionophore (nystatin). This indicates that such changes in physiological state do not alter the efficiency of DQF signal generation in human RBCs.

Animals↗
PubMed2003

Modelling biological invasions: species traits, species interactions, and habitat heterogeneity.

In this paper we explore the integration of different factors to understand, predict and control ecological invasions, through a general cellular automaton model especially developed. The model includes life history traits of several species in a modular structure interacting multiple cellular automata. We performed simulations using field values corresponding to the exotic Gleditsia triacanthos and native co-dominant trees in a montane area. Presence of G. triacanthos juvenile bank was a determinant condition for invasion success. Main parameters influencing invasion velocity were mean seed dispersal distance and minimum reproductive age. Seed production had a small influence on the invasion velocity. Velocities predicted by the model agreed well with estimations from field data. Values of population density predicted matched field values closely. The modular structure of the model, the explicit interaction between the invader and the native species, and the simplicity of parameters and transition rules are novel features of the model.

Computer Simulation↗
PubMed2004

Connecting the dots between genes, biochemistry, and disease susceptibility: systems biology modeling in human genetics.

Understanding how DNA sequence variations impact human health through a hierarchy of biochemical and physiological systems is expected to improve the diagnosis, prevention, and treatment of common, complex human diseases. We have previously developed a hierarchical dynamic systems approach based on Petri nets for generating biochemical network models that are consistent with genetic models of disease susceptibility. This modeling approach uses an evolutionary computation approach called grammatical evolution as a search strategy for optimal Petri net models. We have previously demonstrated that this approach routinely identifies biochemical network models that are consistent with a variety of genetic models in which disease susceptibility is determined by nonlinear interactions between two or more DNA sequence variations. We review here this approach and then discuss how it can be used to model biochemical and metabolic data in the context of genetic studies of human disease susceptibility.

Computational Biology↗
PubMedDate not supplied

Diagrammatic representations for modelling biological knowledge.

The contemporary research and development context in multidisciplinary biology has a serious requirement for integrating knowledge from disparate sources, and facilitating much-needed inter- and intra-disciplinary dialogue. A multiplicity of models arises when pluralistic approaches to modelling are followed, and also when there is not only a requirement to model systems and data, but also knowledge of systems and data. The challenges of addressing this multiplicity do not only include articulating the structure of complex systems, but also placing modelling within the framework of a process as well as a product. The graph representations presented here facilitate dialogue, modelling, clarification and specification of concepts, and the sharing of terms. This paper explores relationships between collections of graph representations. It is hoped that in future, when readers look at a node or a process in a graph, they will have a much deeper appreciation of relationships and context.

Data Display↗
PubMed2004

Biological models for leukaemia and lymphoma.

Blood-cell cancers (leukaemias, lymphomas and myeloma) are a very diverse group of neoplasms derived from a variety of stem cells at different hierarchical levels of haemopoietic and lymphoid cell development. This biological heterogeneity is likely to be associated with a variety of different etiological mechanisms. Correspondingly, a large number of inherited normal allelic variations might be expected to contribute to risk. Leukaemias alone have more than 200 different acquired (non-constitutive) molecular abnormalities but some are much more prevalent than others and are associated with biological subtypes with distinctive clinical or prognostic features. Balanced chromosome translocations are very common, together with simple gains or losses of chromosomes. Gene deletions and mutations are also relatively common, especially in more advanced disease. In several types of leukaemia and lymphoma, a transition from benign to malignant status can be tracked together with concurrent accrual of additional molecular abnormalities (e.g. chronic myeloid leukaemia evolving into blast crisis and follicular lymphoma becoming diffuse). The covert preclinical natural history of paediatric leukaemia has been revealed by 'back-tracking' using chromosomal translocation-gene-rated fusion gene sequences as clone-specific stable, specific and sensitive markers. Studies in identical twins, in archived neonatal blood spots of patients and in normal newborn cord bloods all support the contention that chromosomal translocations often initiate leukaemia in utero. Twin concordance rates (and animal modelling) suggest that further secondary genetic changes and exposures postnatally are, however, critical and this is endorsed by the finding that leukaemic fusion genes are present in normal newborn infants at a rate that far exceeds the cumulative risk of leukaemia. The natural history of leukaemic subtypes provides a useful framework for molecular epidemiological studies and significant advances have been made in this respect with infant and childhood acute lymphoblastic leukaemia.

Embryonic and Fetal Development↗
PubMed1996

[Comments on the suitability of swine skin as a biological model for human skin].

The use of porcine skin as a biomedical model for the human integument is discussed with reference to the literature. The epidermis and dermis can be used as a model as there are clear structural, functional and biochemical similarities with human skin layers. The actual utilization of porcine skin in dermatological research is reviewed. Practical difficulties are emphasized: in particular, the conditions required for use of porcine skin in experimental research, the most suitable breeds, and restrictions on biological interpretation of the results.

Animals↗
PubMed2007

On the theory of reactive mixtures for modeling biological growth.

Mixture theory, which can combine continuum theories for the motion and deformation of solids and fluids with general principles of chemistry, is well suited for modeling the complex responses of biological tissues, including tissue growth and remodeling, tissue engineering, mechanobiology of cells and a variety of other active processes. A comprehensive presentation of the equations of reactive mixtures of charged solid and fluid constituents is lacking in the biomechanics literature. This study provides the conservation laws and entropy inequality, as well as interface jump conditions, for reactive mixtures consisting of a constrained solid mixture and multiple fluid constituents. The constituents are intrinsically incompressible and may carry an electrical charge. The interface jump condition on the mass flux of individual constituents is shown to define a surface growth equation, which predicts deposition or removal of material points from the solid matrix, complementing the description of volume growth described by the conservation of mass. A formulation is proposed for the reference configuration of a body whose material point set varies with time. State variables are defined which can account for solid matrix volume growth and remodeling. Constitutive constraints are provided on the stresses and momentum supplies of the various constituents, as well as the interface jump conditions for the electrochemical potential of the fluids. Simplifications appropriate for biological tissues are also proposed, which help reduce the governing equations into a more practical format. It is shown that explicit mechanisms of growth-induced residual stresses can be predicted in this framework.

Animals↗