A computationally efficient approximation to the nearest neighbor interchange metric

The nearest neighbor interchange (nni) metric is a distance measure providing a quantitative measure of dissimilarity between two unrooted binary trees with labeled leaves. The metric has a transparent definition in terms of a simple transformation of binary trees, but its use in nontrivial problems is usually prevented by the absence of a computationally efficient algorithm. Since recent attempts to discover such an algorithm continue to be unsuccessful, we address the complementary problem of designing an approximation to the nni metric. Such an approximation should be well-defined, efficient to compute, comprehensible to users, relevant to applications, and a close fit to the nni metric; the challenge, of course, is to compromise these objectives in such a way that the final design is acceptable to users with practical and theoretical orientations. We describe an approximation algorithm that appears to satisfy adequately these objectives. The algorithm requires O(n) space to compute dissimilarity between binary trees withn labeled leaves; it requires O(n logn) time for rooted trees and O(n ² logn) time for unrooted trees. To help the user interpret the dissimilarity measures based on this algorithm, we describe empirical distributions of dissimilarities between pairs of randomly selected trees for both rooted and unrooted cases.The Natural Sciences and Engineering Research Council of Canada partially supported this work with Grant A-4142.     

Epidemiological evidence for causal relationship between Epstein-Barr virus and Burkitt's lymphoma from Ugandan prospective study.

Results from a prospective sero-epidemiological study initiated in Uganda in 1971 indicate that children with high antibody titres to Epstein-Barr virus structural antigens are at high risk of developing Burkitt's lymphoma. These findings strongly support a causal relationship between the Epstein-Barr virus and Burkitt's lymphoma but suggest that the oncogenic potential of the virus is realised only in exceptional circumstances.     

Linkage of a nasopharyngeal carcinoma susceptibility locus to the HLA region

The frequency of nasopharyngeal carcinoma is nearly 100-fold higher in southern Chinese than in most European populations. Earlier studies have suggested that an increased risk of nasopharyngeal carcinoma is associated with specific haplotypes in the HLA region: relative risks slightly over twofold were found for haplotypes A2, Bw46 and the antigen B17. We now report a linkage study based on affected sib pairs which suggests that a gene closely linked to the HLA locus confers a greatly increased risk of nasopharyngeal carcinoma. The maximum likelihood estimate is of a relative risk of approximately 21. The relationship between this suspected disease susceptibility gene (or genes) and known viral and environmental aetiological factors remains to be elucidated.     

Effects of prednisolone and butyrate on agglutinability of HeLa cells by concanavalin A

Cellular and Molecular Life Sciences - Agglutinability by concanavalin A was measured with HeLa65 cells grown with prednisolone or sodium butyrate, 2 compounds that increase the activity of the...     

A comparison of the variability of muscle,hair, lens and plasma proteins

Résumé Trois groupes de protéines structurelles (celles de la lentille, celle des muscles, et celles du poil) furent comparés aux protéines de plasma, en utilisant l'électrophorèse en gel polyacrylamide. Les variations apparaissant chez 4 espèces de rongeurs furent examinées et on trouva que les protéines de plasma varient plus que les autres. L'importance de ces résultats dans la recherche d'une évolution possible de ces protéines est considérée.

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It is a pleasure to thank ProfessorB. C. Clarke, Mrs.R. M. Clayton and Dr.D. E. S. Truman for valuable discussions. This work was carried out during the tenure of a Research Studentship from the Medical Research Council.     

Synthesis of a symmetrical tetrasubstituted cucurbit[6]uril and its host-guest inclusion complex with 2,2′-bipyridine

Synthesis of a symmetrical tetrasubstituted cucurbit[6]uril has been achieved by using the diether of dimethylglycoluril (1) and the dimmer of glycoluril (2). The structure of the symmetrical tetramethylcucurbit[6]uril (TMeQ[6]) has been determined by single crystal X-ray diffraction, ^1H NMR spectroscopy and ESMS. The ^1H NMR spectra of 2,2‘-bipyridine added to TMeQ[6] reveal that the host-guest inclusion complex was easily formed.