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At least 1,189 records · Page 66Linked to original sources
PubMed1984

Computer modelling of cell division during development using a topological approach.

Development in multicellular animals consists of a constant progression of cell division, differentiation and morphogenesis. Our understanding of the relationship between division and the acquisition of shape and form is not well understood, and this paper describes a computer representation of cell division processes with possible applications to the modelling of developmental events. This representation is not itself a model in the true sense, but is a scaffolding onto which a set of model assumptions and parameters can be built. We discuss one such set of assumptions, used to model cell sorting, describe the extension of the framework to represent sheets of cells in three dimensions, and make some observations on the incorporation of mechanical forces into the representation.

Animals↗
PubMed1985

[A discrete-events computer model of fox rabies].

A technique of discrete events simulation is used to construct a model of an epi-enzootic disease of vulpine rabies. Because this technique is easy to use, it makes it possible to take into account different spatial and temporal characteristics of the dynamics of vulpine populations and transmission of rabies. Thereby, the model simulates satisfactorily the epi-enzootic disease of rabies presently observed in France.

Animals↗
PubMed1987

Podophyllotoxin analogues: synthesis and computer modelling investigation of structure-activity relationships.

The conformations of four 2-substituted-4-deoxy-analogues of podophyllotoxin have been studied using data obtained from X-ray structure determinations and molecular modelling studies. In these, root mean square differences between these structures and those of the cytotoxic agents 6'-bromopodophyllotoxin and colchicine were determined. Attempts have been made to correlate structure with the available biological activity data.

Antineoplastic Agents↗
PubMed2004

A new DNA computing model for the NAND gate based on induced hairpin formation.

Hairpin structure of DNA molecules has been widely employed in a variety of biosensors and in nanoscale molecular assembly applications. For example, the well known molecular beacons can report the presence of specific nucleic acids in homogeneous solutions with high accuracy. Recently, Smith et al. proposed the induction of hairpin formation through sequence-specific binding of a small-molecule ligand to a G-G mismatch. Not only did this method offer great flexibility in controlling hairpin formation, more importantly the induced hairpin maintains high degree of sensitivity toward specific hybridization. In this contribution, we present a theoretical model for the logical NAND gate based on induced hairpin formation.

Computer Simulation↗
PubMed1980

A computer model of temperature distribution inside a lossy sphere after microwave radiation.

The temperature distribution inside a lossy sphere resulting from the absorption of microwave energy was approximated by successive numerical iterations. of the thermal energy equation. Heat transfer within the sphere by conduction was considered. In the model energy was not dissipated by convection but was contained in the sphere for over 200 seconds. Exposure of a 5-cm sphere to 3,000 MHz at 30 mW/cm2 for 200 seconds was calculated to produce a temperature rise of 0.56 degrees C near the front surface.

Computers↗
PubMed1987

A computer model of evolutionary optimization.

Molecular evolution is viewed as a typical combinatorial optimization problem. We analyse a chemical reaction model which considers RNA replication including correct copying and point mutations together with hydrolytic degradation and the dilution flux of a flow reactor. The corresponding stochastic reaction network is implemented on a computer in order to investigate some basic features of evolutionary optimization dynamics. Characteristic features of real molecular systems are mimicked by folding binary sequences into unknotted two-dimensional structures. Selective values are derived from these molecular 'phenotypes' by an evaluation procedure which assigns numerical values to different elements of the secondary structure. The fitness function obtained thereby contains nontrivial long-range interactions which are typical for real systems. The fitness landscape also reveals quite involved and bizarre local topologies which we consider also representative of polynucleotide replication in actually occurring systems. Optimization operates on an ensemble of sequences via mutation and natural selection. The strategy observed in the simulation experiments is fairly general and resembles closely a heuristic widely applied in operations research areas. Despite the relative smallness of the system--we study 2000 molecules of chain length v = 70 in a typical simulation experiment--features typical for the evolution of real populations are observed as there are error thresholds for replication, evolutionary steps and quasistationary sequence distributions. The relative importance of selectively neutral or almost neutral variants is discussed quantitatively. Four characteristic ensemble properties, entropy of the distribution, ensemble correlation, mean Hamming distance and diversity of the population, are computed and checked for their sensitivity in recording major optimization events during the simulation.

Base Sequence↗
PubMed1987

Computational model for insensible water loss from the newborn.

A mathematical model for predicting insensible water loss from the newborn infant has been developed, and its adjustable parameters have been evaluated using existing data for respiratory and transepidermal water loss components. Subsequently, the model was verified by using an independent set of available data on total insensible loss from naked infants who were not mechanically ventilated and who did not sweat. Under these conditions, the model was capable of correctly predicting the influence of ambient humidity, gestational age, and postnatal age, and in general, the predictions had a precision of +/- 14%, but they tended to underestimate insensible water loss by -16%. The straightforward algebraic form of the model makes it suitable for computerized calculations, which can be readily available at the bedside and quickly updated to account for changes in infant or environmental variables. The model is useful both for anticipating the abnormally large insensible water loss of the premature infant early in life and for computing expected changes in insensible water loss as a result of intentional manipulation of environmental factors, such as incubator temperature or supplemental humidification.

Computer Simulation↗