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Biomedical subjects

C Lefèvre

Publications and source records attributed to C Lefèvre.

At least 37 records · Page 2Linked to original sources
PubMed1993

The position end-set tree: a small automaton for word recognition in biological sequences.

We consider the basic function which locates a specific string of symbols within a longer sequence. When one is expecting to do many substring searches it is worthwhile to build an auxiliary index to the sequence to aid in the search. We propose a method to generate a compact index that can be viewed as a small (partial) deterministic finite automaton recognizing the subword structure of a sequence. We present an algorithm for its construction on-line in linear time. Such a data structure permits the efficient localization of subwords in a sequence and can be used in the development of interactive sequence analysis software.

Algorithms↗
PubMed1993

Pattern recognition in DNA sequences and its application to consensus foot-printing.

We consider the problem of comparing several nucleic acid sequences to identify words occurring imperfectly (patterns with no gap) with unusual frequency. Methods for computing, representing, and inspecting interactively the structure of such repeating motifs in nucleic acids and more generally any text are described. Multiple sequences are treated as one large concatenate. In a preprocessing step, a lexical index is created to provide rapid string matching for the enumeration of the words matching a pattern. For given word features (word length, minimal frequency), a sequence profile is displayed. The profile can be inspected interactively with on-line algorithms. Applications to the identification of regulatory elements in DNA regions involved in the control of gene expression are presented. Our program ('DNA-Lexemics') runs on the Macintosh.

Algorithms↗
PubMed1993

A small automaton for word recognition in DNA sequences and its application to consensus analysis of regulatory elements in DNA regions controlling gene expression.

A method for pattern analysis of DNA sequence data is considered. A space economical automaton for word recognition was presented elsewhere together with an algorithm for its compilation in linear time. An algorithm for the localization of words including imperfect matches (motif search) was developed. A program was implemented on the Macintosh and used extensively for the representation of the word composition of DNA data. We explore different sets of regulatory sequences to illustrate the performance of this method. In mammalian DNA, this analysis reveals "consensus motifs" corresponding to functional (or putative) cis-acting elements mediating the regulation of gene expression.

Algorithms↗
PubMed1991

The dimension of Reed-Frost epidemic models with randomized susceptibility levels.

A generalized Reed-Frost epidemic process is discussed in which variability among susceptible individuals is incorporated by randomizing the levels of resistance of the individuals to the infection. Our purpose is to derive the exact distribution of the ultimate number of susceptibles surviving the disease. This is achieved by a simple conditional argument and by using a particular family of polynomials defined recursively. The results can be viewed as a continuation of those obtained by the authors for the alternative situation with randomized infectivity levels.

Disease Outbreaks↗
PubMed1991

Measuring the severity of disease clustering using Tango's index.

Tango [Biometrics 40:15 (1984)] proposed an index for detecting disease clustering in time applicable to grouped data obtained from a population that remains fairly stable over the study period. This index has received considerable attention in the literature including the suggestion that it be used to detect the space-time clustering of diseases and the suggestion to use similar test statistics to detect disease clustering in space and/or time while accounting for a changing population size over the study period. This paper concerns the related question of measuring the severity of the disease clustering once it has been determined that cases are not randomly distributed over space and/or time. A family of alternatives to randomness is proposed in which space and/or time versions of Tango's index are sufficient statistics for the parameters measuring the severity of the clustering. For the special case of temporal clustering, an unbiased estimator of the clustering parameter and its sampling variance is derived, and a particularly simple interpretation of this estimator is suggested. These latter results are based on some asymptotic approximations due to Tango [Biometrics 46:351 (1990)]. An application to the trisomy data given by Wallenstein [Am. J. Epidemiol. 111:367 (1980)] is discussed.

Cluster Analysis↗
PubMed1991

A mathematical model of rinderpest infection in cattle populations.

A mathematical model for the epidemiology of rinderpest was developed, starting from a simplified descriptive analysis of the disease. A formula for the calculation of the probability of infection of a susceptible animal was first established. A deterministic failure threshold of the infection was then deduced. Deterministic and stochastic approaches were adopted using iterative methods on a computer. These allowed a description of the spread and the variability of an infection process in a population to be made. An illustration of the use of this model showed that, in some cases, variability effects due to stochastic factors were very important. In these particular conditions, the use of the deterministic model alone was not adequate for a good description of the infection. Consequently, improvements of the model were proposed in order to make it more realistic and to allow its use for the evaluation of the efficiency of field operations.

Animals↗
PubMed1991

[3-dimensional reconstruction of x-ray computed tomographic views in fractures of the acetabulum].

In 21 cases of acetabulum fractures of 19 patients, the authors compare the findings given by three dimensional reconstructions of axial CT scan cuts with the plain films. The number of CT scan cuts is reasonable for each patient. Working time is about 20 to 30 minutes for the technician. In the cases of complex and displaced fractures, three dimensional imaging brings often decisive informations for the therapeutic management of these patients. Unusual views are often allowed but completely adapted to each type of fracture.

Acetabulum↗
PubMed1989

[A proposed prototype for recording and analysis of mandibular movement: the Cinétic].

The investigation of means of recording mandibular movement has aroused the interest of a considerable number of researchers. Their own devices, increasingly ingenious, all display certain advantages and shortcomings. The need for a device more appropriate to the needs of day-to-day odontological use has been felt for some time. By giving a broad explanation of how it works, we have tried to assess the possibilities of the proposed prototype, the Cinetic. It measures movement of the dentalium in all three dimensions simultaneously. Since its reliability, when tested by a study concerning a sample of 40 patients, proved entirely satisfactory, a more sophisticated version was promptly devised. This latest Cinetic allows the ROZENCWEIG dyskinesia index, to be calculated, the FARRAR diagram to be drawn, and the mastication movements to be analysed by giving a visual display of the mandibular opening and closing trajectories, the speed diagram, the duration of the cycle, mandibular velocity and acceleration, and a breakdown of the cycles for each respective side. In order to be fully competitive, the Cinetic lacks the capacity to record and analyse condylar movement. Work on incorporating these features is currently at an experimental stage.

Dental Equipment↗
PubMed1988

The venous hilum of the testis and epididymis: anatomic aspect.

The venous return from the testis is effected by 3 venous pathways: the pampiniform plexus gathrs the centripetal and centrifugal paths of the testis with the marginal vein of the epididymis; the deferential vein accompanies the ductus deferens; and the cremasteric vein travels more superficially between the internal and external spermatic fasciae on its way to the inferior epigastric vein. At the caudal pole of the testicle these different pathways form such close connections as to constitute a real vascular junction.

Adult↗
PubMed1987

[The shelf operation for painful hip dysplasia in adults. Apropos of a continuous series of 230 cases].

230 shelf operations were carried out between 1961 and 1985 for painful acetabular dysplasia or subluxation of the hip. 208 patients have been followed up for more than one year, with 79 for between 10 and 24 years. Substantial relief of pain was obtained in 88%. The benefits of operation usually continue for many years. Factors which may lead to a poor result are advanced age, dislocation of the hip and the presence of marked osteoarthritic changes. The results have been compared with those obtained for Chiari's osteotomy, and the relative indications for the two procedures are discussed.

Acetabulum↗
PubMed1986

Threshold behaviour for a chain-binomial S-I-S infectious disease.

The present paper is concerned with a chain-binomial deterministic model for an infectious disease of the S-I-S type. The model extends the Cooke et al. (1977) and Longini (1980) model in the sense that it accounts for the distribution of the number of contacts made by each susceptible during an infectious period and for the probabilities of infection at the different contacts with infectives. The aim of the work is to investigate under which conditions the disease becomes endemic or not. Some partial results are first derived, but a complete analysis of the threshold behaviour seems very intricate. A more detailed discussion is then presented for the specific case where at least K + 1 contacts with infectives, K greater than or equal to 1 fixed, are required to make a susceptible infected.

Communicable Diseases↗
PubMed1985

[Apropos of 87 dislocations of total hip prostheses].

Eighty seven dislocations were seen in 1571 consecutive total hip replacements, mostly performed through a posterior approach. Nine occurred immediately after operation and most of the remainder within 5 weeks. In 26 cases further dislocation occurred, and in 11 patients another operation was required. The 87 dislocated hips have been compared with the remaining 1484. Factors predisposing to dislocation included revision operations, the experience of the surgeon and proper reconstruction of the abductor musculature. When the hip was deemed unstable at the end of an operation, dislocation occurred on 18 occasions out of 20 such cases. The position of the components in the dislocated hips was compared with that in 100 stable prostheses chosen by random sampling. A vertical acetabular prosthesis, and retroversion of the acetabular and femoral components all favoured dislocation. In 331 replacements with a 22 mm diameter head 29 dislocations were seen (8.7%), whereas in 168 replacements with 32 mm heads, 5 dislocations occurred (2.9%).

Hip Dislocation↗