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PubMed1991

[The differential diagnosis of sarcoidosis of the respiratory organs using mathematical methods and computers].

A system for detecting sarcoidosis has been proposed on the basis of the results of a primary examination, which comprises a combination of programs for determining whether sarcoidosis may occur in various X-ray syndromes (enlarged intrathoracic lymph nodes, disseminated process, infiltrative or pneumonia-like shadow and cavity formation). The system has been developed with the help of a program-algorithm complex which enables one to make the dialogue system of the decision-make support on the basis of statistical methods of "image recognition" containing basic structural elements of the expert systems. Program development proceeds from the findings obtained in 406 patients with sarcoidosis of respiratory organs and 723 patients having similar clinical and X-ray picture of the disease. The diagnostic efficiency of the system was 89% in disseminated processes, 90% in enlarged intrathoracic lymph nodes and cavitary changes, and 96.2% in infiltrative changes.

Diagnosis, Differential↗
PubMed1991

Proline in alpha-helix: stability and conformation studied by dynamics simulation.

Free-energy simulations have been used to estimate the change in the conformational stability of short polyalanine alpha-helices when one of the alanines is replaced by a proline residue. For substituting proline in the middle of the helix the change in free energy of folding (delta delta G degrees) was calculated as 14 kJ/mol (3.4 kcal/mol), in excellent agreement with the one available experimental value. The helix containing proline was found to be strongly kinked; the free energy for reducing the angle of the kink from 40 degrees to 15 degrees was calculated, and found to be small. A tendency to alternate hydrogen bonding schemes was observed in the proline-containing helix. These observations for the oligopeptide agree well with the observation of a range of kink angles (18-35 degrees) and variety of hydrogen bonding schemes, in the rare instances where proline occurs in helices in globular proteins. For substituting proline at the N-terminus of the helix the change in free energy of folding (delta delta G degrees) was calculated as -4 kJ/mol in the first helical position (N1) and +6 kJ/mol in the second helical position (N2). The observed frequent occurrence of proline in position N1 in alpha-helices in proteins therefore has its origin in stability differences of secondary structure. The conclusion reached here that proline may be a better helix former in position N1 than (even) alanine, and thus be a helix initiator may be testable experimentally by measurements of fraction helical conformation of individual residues in oligopeptides of appropriate sequence. The relevance of these results in regards to the frequent occurrence of proline-containing helices in certain membrane proteins is discussed.

Alanine↗
PubMed1989

A parallel implementation of the ALOPEX process.

Optimization techniques have found many applications in science, engineering, and industry. In all applications, the best value of a "cost function" is sought in a well-defined domain; this cost function in general depends on many parameters. An iterative optimization technique has been developed (ALOPEX) that uses feedback in order to optimize the response of a system. The cost function for this process is problem dependent and therefore quite flexible. The method has been applied successfully to different optimization problems such as pattern recognition, receptive field studies in the visual system of animals, curve fitting, etc. We present two special purpose hardware implementations for ALOPEX. The first method takes time O(logN + logm) and uses O(mN2) processing elements. The second method takes O(logN + m) time and uses O(N2) processing elements. Our basic architecture is a binary tree with N2 leaves (equal to the length of the vectors) and therefore had depth O(logN). Different implications of the two approaches will be discussed including similarities with the biological visual process.

Algorithms↗
PubMed1990

Estimation and inference in pharmacokinetic models: the effectiveness of model reformulation and resampling methods for functions of parameters.

It is well known that high parameter estimate correlations and asymptotic variance estimates can cause estimation and inference problems in the analysis of pharmacokinetic models. In this paper we show that analysis of three important functions of pharmacokinetic parameters, the half-life, mean residence time, and the area under the curve, can sometimes be greatly improved by reformulating the model to address collinearity and by using the bootstrap to form confidence intervals. The resultant estimators can be more accurate than the original ones, and resultant confidence intervals can be narrower. Of the three measures, the half-life estimator is much better behaved than the estimators of mean residence time and area under the curve under collinearity, suggesting that it (or measures like it) should be used more often.

Analysis of Variance↗
PubMed1978

Performance of various mathematical methods for computer-aided processing of radioimmunoassay results.

Interpolation and regression methods are available for computer aided determination of radioimmunological end results. We compared the performance of 6 algorithms (weighted and unweighted linear logit log regression; quadratic logit log regression, smoothing spline interpolation with a large and small smoothing factor, respectively, and polygonal interpolation and the manual curve fitting on the basis of three radioimmunoassays with different reference curve characteristics (digoxin, estriol, human chorionic somatomammotrophin (HCS)). Great store was set by the accuracy of the approximation at the intermediate points on the curve, i.e. those points that lie midway between two standard concentrations. These concentrations were obtained by weighing and inserted as unknown samples. In the case of digoxin and estriol the polygonal interpolation provided the best results, while the weighted logit log regression proved superior in the case of HCS.

Computers↗
PubMed1987

Interactive statistical analysis of survival data.

This paper describes a SAS macro which facilitates the interactive analysis of right-censored survival data. Such data commonly occur in medical studies. The program produces Kaplan-Meier survival curves on a wide variety of graphics devices. The program also performs log-rank and generalized Wilcoxon significance tests among all plotted curves and for each pairwise contrast if desired. Because the program is intelligent and does not prompt the user for information that it can independently obtain, it is quite easy to use.

Computer Graphics↗
PubMed1987

Balancing allocation of subjects in biomedical research: a minimization strategy based on ranks.

A new method for ensuring the comparability of groups of experimental subjects is proposed. All subjects are ranked on each measured pretreatment variable and differences between groups in the means and the standard deviations of these ranks are minimized by systematically exchanging subjects when those exchanges yield less imbalance between groups. This method was designed for small studies in which pretreatment data from all subjects are known before the start of the experiment. A series of computer simulations suggests that this procedure is effective in balancing groups on several variables although the amount of computer time required becomes excessive as the number of subjects is increased.

Computer Simulation↗
PubMed1989

A new method for aligning histological serial sections for three-dimensional reconstruction.

A new method for aligning histological serial sections for three-dimensional reconstruction by computer is introduced. This method is particularly suited for embedding structures in celloidine or paraplast. Prior to sectioning, at least three reference markers are affixed to the preparation in a direction perpendicular to the section plane, for easy identification on the finished sections. An algorithm translates and rotates the serial sections until all the reference markers are congruent. The main advantage of this method, however, is its capability to eliminate deformations caused by compression or stretching during sectioning by the determination of correction factors.

Algorithms↗