Biomedical subjects

P Main

Publications and source records attributed to P Main.

13 recordsLinked to original sources

PubMed2000

The use of wavelet transforms in low-resolution phase extension.

A method to extend low-resolution phases has been developed using histogram matching not only of the electron density itself but also of histograms obtained from the different levels of detail provided by the wavelet transform of the electron density. It is shown that the method can extend phases from 10 A to around 6-7 A on a wide range of trial structures differing in size, space group and solvent content. This level of phase extension can improve the electron-density map from little more than a molecular envelope to one in which secondary structure can often be identified.

Bacterial Proteins↗

PubMed2000

Wavelet analysis of electron-density maps.

The wavelet transform is a powerful technique in signal processing and image analysis and it is shown here that wavelet analysis of low-resolution electron-density maps has the potential to increase their resolution. Like Fourier analysis, wavelet analysis expresses the image (electron density) in terms of a set of orthogonal functions. In the case of the Fourier transform, these functions are sines and cosines and each one contributes to the whole of the image. In contrast, the wavelet functions (simply called wavelets) can be quite localized and may only contribute to a small part of the image. This gives control over the amount of detail added to the map as the resolution increases. The mathematical details are outlined and an algorithm which achieves a resolution increase from 10 to 7 A using a knowledge of the wavelet-coefficient histograms, electron-density histogram and the observed structure amplitudes is described. These histograms are calculated from the electron density of known structures, but it seems likely that the histograms can be predicted, just as electron-density histograms are at high resolution. The results show that the wavelet coefficients contain the information necessary to increase the resolution of electron-density maps.

Algorithms↗

PubMed2000

Low-resolution phase extension using wavelet analysis.

A method to extend low-resolution phases is presented which uses histogram matching not only of the electron density, but also of histograms obtained from the different levels of detail provided by the wavelet transform of the electron density. Statistical values for the wavelet coefficients can be predicted and depend only on the resolution and solvent content. Therefore, new details can be added to an electron-density map by matching the values of the wavelet coefficients to those predicted for an increased resolution. The positions of the new details are also guided by the diffraction pattern. In this way, the resolution can be increased gradually; on a number of trial structures of different size, solvent percentage and space group, it has been possible to extend the phasing from 10 A to around 6-7 A.

Electrons↗

PubMed1998

Miscellaneous algorithms for density modification.

Various algorithms are described, developed for the dm density modification package, which have not been described elsewhere. Methods are described for the following problems: determination of the absolute scale and overall temperature factor of a data set, by a method which is less dependent on data resolution than Wilson statistics; an efficient interpolation algorithm for averaging and its application to refinement of averaging operators; a method for the automatic determination of averaging masks.

Algorithms↗

PubMed1998

Health years equivalents as a measurement of preferences for dental interventions.

OBJECTIVE: To test the feasibility and importance of measuring preferences among treatment choices using Healthy Years Equivalents (HYE). DESIGN: Development of scenarios for alternative approaches to caries treatment. Completion of category rating and standard gamble questions elicited in personal interviews. SETTING: The provision of dental care to children in a public-funded dental health clinic. PARTICIPANTS: Random sample of the adult population of Hamilton, Ontario. MAIN OUTCOME MEASURES: The percentage of the sample unable to complete the interviews, time taken to perform interviews, ease of understanding of interviews, correlation between rank ordering and HYE scores. RESULTS: Ninety-six per cent of the sample were able to complete the HYE exercise. Inconsistencies between HYE scores and rank orders implying preference reversal occurred in 6% of those completing HYE scores for the two scenarios. The additional time taken by the HYE was of the order of 17 minutes but increased with the age of the subject. Where problems occurred, they were related to the method of measurement or the sensitivity of the chosen scale as opposed to additional requirements of the HYE. There was some evidence that HYEs and QALYs produced different scores even in the context of chronic constant health states. CONCLUSIONS: HYEs are a feasible and important practical method of measuring preferences among interventions. Alternative utility-based approaches, such as willingness to pay, may be required to detect differences in modest improvements in temporary health states.

Adult↗

PubMed1994

The MAXM hematology autoanalyzer. An alternative?

The MAXM is a compact blood count and differential analyzer that appeals to both the space-limited, full-service laboratory and the large outpatient practice. The authors compared the performance of the Coulter MAXM to the larger Coulter STKS. Linearity and precision studies were comparable to the STKS. MAXM leukocyte differentials were closely correlated with STKS and manual readings, being excellent in the neutrophil, lymphocyte, and eosinophil categories but poorer on monocyte counts. Basophil counts did not correlate with STKS or manual counts. Analyzer suspect flagging was similar in both machines, with the MAXM exhibiting slightly reduced sensitivity and greater specificity. MAXM processing of a single sample requires twice the time. The MAXM functions well for a large office practice and as a backup for large medical laboratories but, because of its hands-on requirements and lack of speed, cannot replace the larger, more automated analyzers.

Autoanalysis↗

PubMed1993