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At least 613 records · Page 34Linked to original sources
PubMedDate not supplied

Continuous time-dependence in computed tomography.

Computed tomography is sensitive to changes in the imaged distribution during acquisition of the projection data. Previous investigations have emphasized discrete or discontinuous changes in the imaged object. Recent advances have motivated our investigation of object time-dependence characterized by a continuous function in time at each point. Formal mathematical and computer simulation approaches have been developed, and are presented along with simple examples of their applications. Further applications in three distinct ongoing studies are outlined.

Computers↗
PubMed1975

Mathematical method to utilize a computer for diagnosis of site and type of intracerebral mass lesions.

A mathematical process has been devised which can utilize full clinical data of symptoms and signs, neuroradiological procedures, EEG and isotope scanning to predict the site and pathological process in a patient presenting with disturbance of central nervous system function. The work is a further expansion and modification of the computer program described by Du Boulay and Price (1968).

Brain Neoplasms↗
PubMed2003

Simplicity: a unifying principle in cognitive science?

Much of perception, learning and high-level cognition involves finding patterns in data. But there are always infinitely many patterns compatible with any finite amount of data. How does the cognitive system choose 'sensible' patterns? A long tradition in epistemology, philosophy of science, and mathematical and computational theories of learning argues that patterns 'should' be chosen according to how simply they explain the data. This article reviews research exploring the idea that simplicity drives a wide range of cognitive processes. We outline mathematical theory, computational results and empirical data that underpin this viewpoint.

Journal Article↗
PubMed1989

In vivo indicator dilution kinetics of PAH transport in dog kidney.

In vivo multiple indicator-dilution (MID) data were analyzed using a computer-assisted mathematical model of transepithelial cell transport to determine p-aminohippuric acid (PAH) transport kinetics across the proximal tubular antiluminal (ALM) and luminal (LM) membranes. A bolus of 125I-labeled albumin (plasma reference), [14C]creatinine (interstitial reference), and tracer [3H]PAH was injected into the left renal artery of anesthetized mongrel dogs (n = 21), and immediate serial sampling of the left renal venous and left and right urine outputs was performed (control). MID runs were then repeated in the same dog following intravenous infusion of unlabeled PAH. For all plasma PAH concentrations ([PAH]P), the steady-state unidirectional flux coefficients were calculated at the ALM and LM. The computer-derived unidirectional flux coefficients were in keeping with active ALM transport and passive, carrier-mediated LM transport. The Km calculated for ALM uptake (interstitium to cell) was 0.51 mM. PAH transport was completely inhibited by probenecid. As [PAH]P increased, the renal vein mean transit time ratio t[3H]PAH/t[14C]creatinine was greater than 1.0, indicating backflux from cells into the interstitium, then declined toward unity, as ALM and LM transport became saturated. This study, which used PAH as a model substrate demonstrated the feasibility of utilizing computer-assisted mathematical models to quantitate the kinetics of transepithelial transport from in vivo experimentation.

Animals↗
PubMed2006

Rules for modeling signal-transduction systems.

Formalized rules for protein-protein interactions have recently been introduced to represent the binding and enzymatic activities of proteins in cellular signaling. Rules encode an understanding of how a system works in terms of the biomolecules in the system and their possible states and interactions. A set of rules can be as easy to read as a diagrammatic interaction map, but unlike most such maps, rules have precise interpretations. Rules can be processed to automatically generate a mathematical or computational model for a system, which enables explanatory and predictive insights into the system's behavior. Rules are independent units of a model specification that facilitate model revision. Instead of changing a large number of equations or lines of code, as may be required in the case of a conventional mathematical model, a protein interaction can be introduced or modified simply by adding or changing a single rule that represents the interaction of interest. Rules can be defined and visualized by using graphs, so no specialized training in mathematics or computer science is necessary to create models or to take advantage of the representational precision of rules. Rules can be encoded in a machine-readable format to enable electronic storage and exchange of models, as well as basic knowledge about protein-protein interactions. Here, we review the motivation for rule-based modeling; applications of the approach; and issues that arise in model specification, simulation, and testing. We also discuss rule visualization and exchange and the software available for rule-based modeling.

Computer Simulation↗
PubMed1989

Numerical calculation of energy deposition by broad high-energy electron beams.

The feasibility is demonstrated of a numerical method to calculate dose deposition by broad high-energy electron beams in homogeneous matter or in heterogeneous matter in which the heterogeneities are arranged in slabs perpendicular to the beam axis. The method is based only on the basic physical interaction processes of high-energy electrons and matter. The method is an extended version of the phase space time evolution method as described by Cordaro and Zucker (1971). The calculated depth-dose curves, energy spectra and angular distributions agree very well with results of the extensive class II Monte Carlo calculations of Andreo and Brahme (1984) and Andreo (1985), but require much less computer time: typically 3 minutes on a VAX 785 with floating point accelerator. This demonstrates the power of a numerical method in comparison with Monte Carlo methods.

Electrons↗
PubMedDate not supplied

[Characteristics of the shape of auto- and cross-correlation histograms of the spike trains of polysynaptically connected neurons].

Peculiarities of auto- and cross-correlation histograms of spike trains of polysynaptically (disynaptically) connected neurones were studied by means of mathematical and biomathematical modelling of neuronal interaction (computer controlled experiment with neurones of a mollusc) in wide physiological diapazons of the values of parameters characterizing the properties and conditions of functioning of the neurones and synapses. A comparison was carried out of manifestations of polysynaptic and corresponding monosynaptic connections in auto- and cross-correlation histograms.

Action Potentials↗
PubMed1991

Cardiac electrophysiological experiments in numero, Part III: Simulation of arrhythmias and pacing.

This paper is the third and final part of a series of articles reviewing mathematical and computer models of the electrophysiological processes. This section reviews the arrhythmia simulation and discusses models of arrhythmogenic processes, fibrillation and defibrillation, and of heart-pacemaker interaction. The models of arrhythmogenesis are classified into three main sections: models of reentry and vortex reentry, models of myocardial electrotonic interactions, and models of macroreentrant supraventricular tachycardias. This final part of the review discusses the future potential of mathematical and computer models of different cardiac processes.

Arrhythmias, Cardiac↗
PubMed1992

A mathematical model for the computation of the forces exerted by the facial orthopedic mask.

This study presents a model for the computation of the forces exerted on the chin and on the forehead by the facial orthopedic mask in skeletal Class III malocclusions. Cephalometric data as well as geometry of the mask are taken into account to simulate in quantitative terms the entire approach. A computer program has been implemented to validate the model on a group of patients. Despite the approximations about the mechanical characteristics of the appliance and of the constraints (rigid body, ideal constraints) and despite the unavoidable errors in the estimation of the geometric parameters (dimensions and angles), it is shown that the computation of the forces (in orientation and in magnitude) at the forehead and at the chin is possible. Some practical applications of the model are presented.

Adolescent↗
PubMedDate not supplied

Physicians' accuracy in manual computation.

Parenteral alimentation fluids are now part of routine nutritional support in the neonatal intensive care unit, and a number of software products are available to help physicians with the formulations. Use of these products is based on the assumption that an appreciable amount of error occurs during manual computation, but few attempts to measure this error have been reported. I performed a retrospective analysis of the accuracy of physicians' calculations of the formulas for parenteral alimentation fluid. In addition, I assessed the ability of our institution's computer-based parenteral alimentation program to correct the deficiencies identified. The study showed no significant differences between physicians' calculations as a whole and their paired ideal values. Individual errors did occur, however, and were large enough to have potential clinical importance. Use of the parenteral alimentation program was found to correct these errors.

Data Interpretation, Statistical↗
PubMed1989

Precise water vapor pressure value calculations.

Precise values for water vapor pressure in saturated systems may be computed using the Goff-Gratch equation. This equation has been adapted for convenient use on microcomputers. A Microsoft BASIC listing of the programming version of the equation is presented. This BASIC version may be easily translated into other high level programming languages and thus is suitable for use on many computer systems for routine laboratory computations.

Manometry↗
PubMed1988

Neurobiological approach to computing devices.

According to the old metaphor of classical cybernetics the brain can be considered as a computer. Newer theoretical endeavours reverse the question and ask: what could neurobiology offer to engineers of near-future generation computer systems? Three not completely disjoint abstract functions of the nervous system, namely pattern formation, pattern recognition and action, can be treated in a unified conceptual framework. Storage and retrieval mechanisms of information are connected to fault-tolerant, adaptive parallel structures. "Learning" and "plastic behaviour" are interpreted in terms of the theory of non-linear dynamic systems. As neural development and plasticity can be approached by deterministic models superimposed by random influence, noise might also have a positive role to play during the operation of technical computing devices. Molecular computation is discussed in relation to eventual hardware realization of "neurobiology-based" computers.

Cybernetics↗
PubMed1985

Microcomputer programs for the evaluation of predictable long-term exposure.

Some methods proposed for evaluation of predictable long-term exposure by statistical treatment of workshift exposure values are considered. Predictable long-term exposure is a useful parameter for risk assessment procedures, as it allows the evaluation of workplace hazards by taking into account interday variability of exposure to air contaminants. Statistical calculations required for evaluating predictable long-term exposure may be performed easily by hand-held programmable calculators. The programs reported here are for use with a Texas Instruments TI-59 hand-held programmable calculator equipped with a PC-100 C thermal printer. They are designed for users inexperienced in programming, since an interactive approach has been adopted that helps communication between user and computer.

Environmental Exposure↗
PubMed1988

A personal computer-based arrhythmia generator based on mathematical models of cardiac arrhythmia.

A personal computer-based arrhythmia generator has been developed based upon mathematical models of modulated parasystole and the related equations. A system of nonlinear difference equations is used to generate the time series of RR intervals of ECG that contain normal as well as ectopic QRS waves. The ECG waveform is synthesized according to the computed RR interval and the type of QRS wave and output via DA converter in a real-time base. Various types of ECGs with ventricular ectopic beats and those with very long periods were generated by selecting values for a small number of model parameters. This method requires neither large RAM nor external memory for storing a library of arrhythmic ECGs. The theory, hardware design, software implementation on a personal computer, and experimental reconstruction of clinical ECGs based on the model are discussed.

Arrhythmias, Cardiac↗
PubMed1998

First partial three-dimensional model of human monoamine oxidase A.

A survey of the major known structural aspects of monoamine oxidase (MAO) is given and a first partial model of human MAO A is presented. This 3D model has been established using secondary structure predictions and fold recognition methods. It shows two alpha/beta domains (the FAD-binding N-terminal and central domains) and an alpha+beta domain. The C-terminal region is predicted to be responsible for anchoring the protein into the mitochondrial membrane and was not modeled. The covalent binding of the flavin cofactor to a cysteine residue is well predicted. The model is validated with experimental data from the literature and should be useful in designing new experimental studies (site-directed mutagenesis, chemical modification, specific antibodies). This first step towards the 3D structure of monoamine oxidase should contribute to a better understanding of the mechanisms of action and inhibition of this drug target in the treatment of clinical depression.

Amino Acid Sequence↗
PubMed1996

Two sample comparison for large groups of correlated binary responses.

Although there is much literature on testing the treatment effect in experiments with correlated binary outcomes, the existing methodologies only work well when the cluster size is small. In this paper, I propose a simple method to test the treatment effect in experiments with large groups of correlated binary outcomes. I use the weighted estimating equations approach to estimate the treatment effect. The proposal is appropriate under any correlation structure. Power comparisons show the advantage of the new procedure.

Computer Simulation↗
PubMed1999

Computational investigations of structural changes resulting from point mutations in a collagen-like peptide.

The results of 0.5-1.0 ns molecular dynamics simulations of the collagen-like peptides [(POG)4(POA)(POG)4]3 and [(POG)9]3 (POG: proline-hydroxyproline-glycine) are presented. All simulations were performed using the AMBER-94 molecular mechanical force field with a shell of TIP3P waters surrounding the peptides. The initial geometries for the collagen-like peptides included an x-ray crystallographic structure, a computer-generated structure, a [(POG)9]3 structure modeled from the x-ray structure, and the x-ray structure with crystallographic waters replaced with a shell of modeled TIP3P waters. We examined the molecular dynamics peptide residue rms deviation fluctuations, dihedral angles, molecular and chain end-to-end distances, helical parameters, and peptide-peptide and peptide-solvent hydrogen-bonding patterns. Our molecular dynamics simulations of [(POG)4(POA)(POG)4]3 show average structures and internal coordinates similar to the x-ray crystallographic structure. Our results demonstrate that molecular dynamics can be used to reproduce the experimental structures of collagen-like peptides. We have demonstrated the feasibility of using the AMBER-94 molecular mechanical force field, which was parameterized to model nucleic acids and globular proteins, for fibril proteins. We provide a new interpretation of peptide-solvent hydrogen bonding and a peptide-peptide hydrogen bonding pattern not previously reported in x-ray studies. Last, we report on the differences; in particular with respect to main-chain dihedral angles and hydrogen bonding, between the native and mutant collagen-like peptides.

Collagen↗