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Biomedical subjects

W H Day

Publications and source records attributed to W H Day.

11 recordsLinked to original sources
PubMed1992

Threshold consensus methods for molecular sequences.

We introduce a parameterized threshold consensus method (th chi) for molecular sequences which is based on a majority-rule voting principle. In contrast to other frequency-based methods, the th chi method uses a single criterion to return ambiguity codes of different lengths. We derive basic features of the method and establish that it returns at most two ambiguity codes at any position of the consensus sequence. We bound from below the size of the frequency gap that exists when the th chi method returns an ambiguity code. Using such properties, we compare the th chi method to other consensus methods for molecular sequences which are defined in terms of threshold or gap criteria.

Base Sequence↗
PubMed1992

Critical comparison of consensus methods for molecular sequences.

Consensus methods are recognized as valuable tools for data analysis, especially when some sort of data aggregation is desired. Although consensus methods for sequences play a vital role in molecular biology, researchers pay little heed to the features and limitations of such methods, and so there are risks that criteria for constructing consensus sequences will be misused or misunderstood. To understand better the issues involved, we conducted a critical comparison of nine consensus methods for sequences, of which eight were used in papers appearing in this journal. We report the results of that comparison, and we make recommendations which we hope will assist researchers when they must select particular consensus methods for particular applications.

Algorithms↗
PubMed1992

Interpreting consensus sequences based on plurality rule.

Our goal is to help researchers interpret the results of a function, based on the concept of plurality rule, that calculates a consensus of a profile of molecular bases. By expressing the plurality rule function as a composition of simpler functions, we obtain both an algorithm to calculate the consensus result and an upper bound on the number of nonequivalent results. Consequently, when used to analyze molecular sequences such as DNA or RNA, the plurality rule function yields at most 48 nonequivalent consensus results. For problems of reasonable size, we describe an algorithm to calculate the probability that each consensus result would occur if the bases were equally likely to appear at every position of the plurality rule function's input profile.

Algorithms↗
PubMed1990

The Roper-Day total shoulder replacement.

A simple unconstrained shoulder prosthesis has been used in 22 patients (25 shoulders) with incapacitating pain and severely damaged joints who, because of age or generalised rheumatoid disease, have limited functional requirements. All reported good and lasting pain relief. Improvement in range of movement was modest, but there was marked improvement in function. In this group of patients, rotator cuff damage is common, but does not preclude a satisfactory result.

Activities of Daily Living↗
PubMed1987

Computational complexity of inferring phylogenies from chromosome inversion data.

In systematics, parsimony methods construct phylogenies, or evolutionary trees, in which characters evolve with the least evolutionary change. The chromosome inversion, or polymorphism, parsimony criterion is used when each character of a population may exhibit homozygous or heterozygous states, but when the heterozygous state must evolve uniquely. Variations of the criterion concern whether or not the ancestral states of characters are specified. We establish that problems of inferring phylogenies by these criteria are NP-complete and thus are so difficult computationally that efficient optimal algorithms for them are unlikely to exist.

Algorithms↗
PubMed1978

Mechanical tests on the tibial components of non-hinged knee prostheses.

Cadaveric knees replaced with the Geomedic, ICLH, Marmor and Total Condylar prostheses were tested in axial compression, in rotation and in hyperextension in order to observe the strength of fixation of the tibial components. In axial compression the strengths at failure varied widely, both with any one prosthesis and between prostheses. This is attributed largely to the strength of the cancellous bone of the tibia, which was measured in each case and also varied widely. Three natural knees failed at loads of 7300, 7600 and 8300 newtons respectively, whereas the strengths of replaced knees ranged from 3000 to 15750 newtons. At least one example of each design failed at less than 7300 newtons, suggesting little or no reserve of strength. The strength of fixation was greater when the tibial prosthesis was large enough to rest on the whole cross-section of the tibia. In rotation the three prostheses embodying rollers in troughs were stiffer than the Marmor which had a nearly flat tibial-bearing surface. The presence or absence of the cruciate ligaments had a negligible effect on torsional stiffness. In hyperextension, knees replaced with the ICLH, Marmor and Total Condylar prostheses failed by rupture of the posterior capsule at moments of about 60 newton-metres, compared with about 100 for natural knees. With the Marmor prosthesis the anterior cruciate ligament was avulsed at about 20 newton-metres compared with about 75 in natural knees, suggesting that in this respect the retention of the cruciate ligaments contributes little. None of the four knees tested after inserting a Geomedic prosthesis showed strengths as high as those replaced with the other three designs.

Humans↗
PubMed1978

ICLH arthroplasty of the knee: 1968--1977.

The essentially satisfactory results from the ICLH implant as used until 1975 were marred by examples of loosening and sinking of the tibial implant, by patellar pain of varying severity, by wear of the tibial implant caused by fragments of cement and by failure consistently to control the alignment of the leg. This report describes the methods now being used to overcome these complications and gives an account of the success so far achieved.

Arthroplasty↗
PubMed1975

Contact pressures in the loaded human cadaver hip.

The purpose of the work described was to find the average pressure on each of several areas of the acetabular cartilage of the cadaver hip under physiological loads. By obtaining load-deflection curves for one chosen area of cartilage, firstly with all the cartilage present and then after the successive removal of other areas, the fractions of the original load carried by the several areas were found, and hence the average pressures on those areas. Seventeen hips (age range twenty-two to eighty-seven years) were examined. Local pressures varied from zero to 3.4 times the average pressure in each hip. The highest pressures in the series (about 4 to 5 megaNewtons per square metre) were on the areas of thin fibrocartilage which were identified at the zenith of certain acetabula. The results are too few to establish whether or not the pressure distribution was age-related. The higher pressures found are within the range which in other experiments has led to fatigue failure of femoral head cartilage, and it is suggested that hips in which such pressures exist under loads of three times body weight may be predisposed to osteoarthritis.

Acetabulum↗