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Biomedical subjects

R Urbanczik

Publications and source records attributed to R Urbanczik.

At least 19 recordsLinked to original sources
PubMed2001

Universal learning curves of support vector machines.

Using methods of statistical physics, we investigate the role of model complexity in learning with support vector machines (SVMs), which are an important alternative to neural networks. We show the advantages of using SVMs with kernels of infinite complexity on noisy target rules, which, in contrast to common theoretical beliefs, are found to achieve optimal generalization error although the training error does not converge to the generalization error. Moreover, we find a universal asymptotics of the learning curves which depend only on the target rule but not on the SVM kernel.

Journal Article↗
PubMed2001

Efficiently learning multilayer perceptrons.

A learning algorithm for multilayer perceptrons is presented which is based on finding the principal components of a correlation matrix computed from the example inputs and their target outputs. For large networks our procedure needs far fewer examples to achieve good generalization than traditional on-line algorithms.

Algorithms↗
PubMed2000

Online learning with ensembles.

Supervised online learning with an ensemble of students randomized by the choice of initial conditions is analyzed. For the case of the perceptron learning rule, asymptotically the same improvement in the generalization error of the ensemble compared to the performance of a single student is found as in Gibbs learning. For more optimized learning rules, however, using an ensemble yields no improvement. This is explained by showing that for any learning rule f a transform f exists, such that a single student using f has the same generalization behavior as an ensemble of f students.

Humans↗
PubMed1995

[Therapeutic approaches in diseases caused by mycobacteria].

Following the historical introduction (the review by Schlossberger, 1928) the evolution of individual chemotherapy phases is briefly discussed. Then after following points are discussed. 1) The usual controlled clinical trials for evaluation of new drugs must be replaced (perhaps by estimates of the "early bactericidal activity" and of the 2 months' sputum conversion rates). 2) Interesting and of importance are research activities connected with the reasons for properties of TB bacilli in the persistence state, and of drugs capable to combat such bacilli (metronidazole?). 3) Since the human immunity against TB normally operates well (from 100 infected approximately 10 will get a clinically manifest disease), it is necessary to investigate possible combinations of chemo- and immunotherapy, either of combinations of antituberculous and immunomodulating drugs (eg. TNF alpha-antagonists), or of chemotherapy combined with vaccination (eg. M. vaccae). 4) There are still unsolved problems in formulations of drugs (particularly R in fixed combinations) and of drug resorption (in HIV-pos. patients). 5) Other points of research interest could be the adsorption of TB bacilli on the surface of mammalian cells (1st step in pathogenesis), drugs other than antituberculotics (eg. amoxycillin + clavulanic acid), or even drugs used for completely other diseases (eg. antidepressive). 6) All these attempts should serve primarily the purpose of further reduction of the necessary therapy duration (M+ pulmonary TB) to 1 - 2 months in total.

AIDS-Related Opportunistic Infections↗
PubMed1994

[The Mycobacteria Working Group: Investigation of resistance of tuberculosis bacteria in Germany 1991 and 1992].

A tuberculosis caused by resistant or even multidrug-resistant TB bacilli seems to be of increasing importance in some parts of the world. An exact investigation of rates of initial and acquired drug resistance of tubercle bacilli for the whole state of Germany is--considering the corresponding technical, logistic and economic necessities--rather demanding. The "Arbeitskreis Mykobakterien" performed therefore, as a first step, an estimation of global resistance rates of tubercle bacilli in Germany based on questionnaires sent to TB laboratories throughout the country: only the first strain isolated in a patient in 1991 and 1992 should have been considered. The results are presented in Table 1.

Antitubercular Agents↗
PubMed1994

[Is there a reliable new diagnostic procedure in mycobacterial infections including tuberculosis?].

Microscopy remains, for various reasons, even today the most important diagnostic tool for pulmonary TB. Because of the need to monitor drug resistance rates (pulmonary TB) and with other forms of TB or other mycobacterioses radiometric culture techniques, particularly if combined with conventional egg media cultures and with identification of grown bacilli using genetic probes are required on a broad scale; the speed of complete investigation is of utmost importance. Thus, even susceptibility testing should be performed with the radiometric technique. Serology, so far, is unfortunately still incapable of clear-cut answers. This applies also--for the time being--to polymerase chain reaction and other techniques in the field of molecular biology: the sensitivity, specificity and predictive values of such techniques are still not sufficiently high to warrant unequivocal results. This applies also to novel drug resistance tests e.g. luciferase techniques or genetic probes for resistance genes.

Antitubercular Agents↗
PubMed1991

Isoniazid protects mice against endotoxin lethality without influencing tumor necrosis factor synthesis and release.

Treatment of NMRI mice with isoniazid (INH; 25 mg/kg) intraperitoneally induced significant protection when it was injected before or after a lethal intravenous challenge with endotoxin. The INH preparation used was not contaminated with endotoxin. Tumor necrosis factor (TNF) was not elevated in sera from NMRI mice 2 h after the injection of INH. INH did not influence TNF synthesis or release determined in human monocytes in vitro. Therefore, it is concluded that the protective effect of INH against lethal endotoxin is not due to a suppressive effect of INH on TNF production.

Animals↗
PubMed1985

Present position of microscopy and of culture in diagnostic mycobacteriology.

The relative merits of microscopy and culture are discussed; it is attempted to review the possible reasons why microscopy is considered as unreliable in TB diagnosis, including the probably false application of Bayes' theorem. In the author's opinion, microscopy still holds a firm position in the rapid and relatively reliable detection of pulmonary TB. As for culture, it is highly questionable if "better media" could accelerate the growth rate of tubercle bacilli. Therefore, it should be attempted to introduce novel techniques which will allow to decrease considerably the mycobacterial mass needed for detection. Laboratories equipped with such devices could offer their services even on an intercontinental basis, in order to have a favourable cost-benefit ratio.

Bacteriological Techniques↗
PubMed1985

On the possibility of cross-resistance between rifampicin and clofazimine in mycobacteria--a laboratory study.

One-way cross-resistance to rifampicin in clofazimine-resistant substrains of Mycobacterium smegmatis ATCC 607 was seen in 4 instances, whereas at most a borderline situation (probably within the experimental error) occurred in this respect with Mycobacterium parafortuitum 16009 and with strains of Mycobacterium "lufu" and Mycobacterium fortuitum. Clofazimine-resistant sub-strains were not isolated from the parental strains of Mycobacterium tuberculosis. Methodological influences (the gradient plate technique was used in this study) are discussed.

Clofazimine↗