Pattern recognition methods, particularly the 'unsupervised learning' techniques, are well suited for the preliminary analysis of the large data sets produced by computer chemistry. The use of linear and non-linear display methods for such exploratory analysis are exemplified with the aid of two data sets of biologically active molecules. Advantages and disadvantages of these techniques are discussed.

Computer Simulation↗

PubMed1989

Critical density fluctuations in lipid bilayers detected by fluorescence lifetime heterogeneity.

The heterogeneity of the decay of the fluorescence of transparinaric acid in single-component lipid bilayers at temperatures above their gel/liquid crystalline phase transition is shown to be due to the presence of regions of higher local density and higher acyl chain order than the predominant fluid regions. This conclusion is based on selective excitation behavior and the observation of time-resolved fluorescence anisotropies that increase at long times. The fractional amplitude of the long lifetime component of the fluorescence shows a temperature variation that conforms to conventional descriptions of critical behavior. The critical exponent extracted from this variation is 1.1, close to the value of 1.0 that describes ultrasonic data. We therefore conclude that liquid crystalline lipid bilayers exhibit critical behavior with significant density and order fluctuations. This behavior must be taken into account in the interpretation of fluorescence and other spectroscopic measurements of the properties of bilayers.

Kinetics↗

PubMed1989

Analysis of the anisotropy decay of trans-parinaric acid in lipid bilayers.

An analysis is presented of the complex anisotropy behavior of trans-parinaric acid in single component DEPC lipid bilayers. It is shown that a model involving two species with distinct lifetime and motional behavior is required, and is adequate, to explain the observed data. In particular, the observed increase in the anisotropy at long times demonstrates the presence of a species with a long fluorescence lifetime that has a high anisotropy. The time dependence of the anisotropy for these two environments is treated using both a purely mathematical sum of exponentials and a constrained fit based on an approximate solution of the anisotropic diffusion problem. In this latter model the anisotropy is described in terms of the second and fourth rank order parameters, (P2) and (P4), and a single dynamical parameter, D1, the perpendicular diffusion coefficient for this uniaxial probe. The parameters of both models are accurately determined from the fits to the data when two environments coexist and an association is made between lifetime components and distinct rotational sites. The values of the parameters obtained demonstrate the "solid-like" and "fluidlike" nature of these two coexisting environments.

Fatty Acids, Unsaturated↗

PubMed1989

Consultant forum ... the future of information and communications systems.

Explore the source record for details and available documents.

Forecasting↗

PubMed1989

Consultant forum ... questions about the future of information and communication systems.

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Computer Communication Networks↗

PubMed1989

Acetylator phenotype and short-course chemotherapy for tuberculosis in Papua New Guinea.

In Papua New Guinea the slow acetylator phenotype is unusual and peripheral neuropathy during isoniazid therapy is uncommon. Acetylator status and other factors influencing isoniazid-induced peripheral neuropathy are discussed, and statistics from Papua New Guinea are presented. The relevance of acetylator phenotype to other side-effects of isoniazid is less well defined. Prophylactic pyridoxine supplementation during short-course chemotherapy for tuberculosis is not generally necessary in the daily 'A' regimen, but should be maintained in the twice-weekly (high-dose isoniazid) 'B' regimen for adults and children over 20 kg.

Acetylation↗

PubMed1988