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Biomedical subjects

W Kinzel

Publications and source records attributed to W Kinzel.

At least 19 recordsLinked to original sources
PubMed2002

Secure key-exchange protocol with an absence of injective functions.

The security of neural cryptography is investigated. A key-exchange protocol over a public channel is studied where the parties exchanging secret messages use multilayer neural networks which are trained by their mutual output bits and synchronize to a time dependent secret key. The weights of the networks have integer values between +/-L. Recently an algorithm for an eavesdropper which could break the key was introduced by [A. Shamir, A. Mityagin, and A. Klimov, Ramp Session (Eurocrypt, Amsterdam, 2002)]. We show that the synchronization time increases with L2 while the probability to find a successful attacker decreases exponentially with L. Hence for large L we find a secure key-exchange protocol which depends neither on number theory nor on injective trapdoor functions used in conventional cryptography.

Journal Article↗
PubMed2001

Multichoice minority game.

The generalization of the problem of adaptive competition, known as the minority game, to the case of K possible choices for each player, is addressed, and applied to a system of interacting perceptrons with input and output units of a type of K-state Potts spins. An optimal solution of this minority game, as well as the dynamic evolution of the adaptive strategies of the players, are solved analytically for a general K and compared with numerical simulations.

Journal Article↗
PubMed2001

Generation of unpredictable time series by a neural network.

A perceptron that "learns" the opposite of its own output is used to generate a time series. We analyze properties of the weight vector and the generated sequence, such as the cycle length and the probability distribution of generated sequences. A remarkable suppression of the autocorrelation function is explained, and connections to the Bernasconi model are discussed. If a continuous transfer function is used, the system displays chaotic and intermittent behavior, with the product of the learning rate and amplification as a control parameter.

Journal Article↗
PubMed2000

Interacting neural networks.

Several scenarios of interacting neural networks which are trained either in an identical or in a competitive way are solved analytically. In the case of identical training each perceptron receives the output of its neighbor. The symmetry of the stationary state as well as the sensitivity to the used training algorithm are investigated. Two competitive perceptrons trained on mutually exclusive learning aims and a perceptron which is trained on the opposite of its own output are examined analytically. An ensemble of competitive perceptrons is used as decision-making algorithms in a model of a closed market (El Farol Bar problem or the Minority Game. In this game, a set of agents who have to make a binary decision is considered.); each network is trained on the history of minority decisions. This ensemble of perceptrons relaxes to a stationary state whose performance can be better than random.

Algorithms↗
PubMed1999

Receiver operating characteristics of perceptrons: influence of sample size and prevalence.

In many practical classification problems it is important to distinguish false positive from false negative results when evaluating the performance of the classifier. This is of particular importance for medical diagnostic tests. In this context, receiver operating characteristic (ROC) curves have become a standard tool. Here we apply this concept to characterize the performance of a simple neural network. Investigating the binary classification of a perceptron we calculate analytically the shape of the corresponding ROC curves. The influence of the size of the training set and the prevalence of the quality considered are studied by means of a statistical-mechanics analysis.

Biophysical Phenomena↗
PubMed1998

Antipredictable sequences: harder to predict than random sequences.

For any discrete-state sequence prediction algorithm A, it is always possible, using an algorithm B no more complicated than A, to generate a sequence for which A's prediction is always wrong. For any prediction algorithm A and sequence x, there exists a sequence y no more complicated than x, such that if A performs better than random on x, then it will perform worse than random on y by the same margin. An example of a simple neural network predicting a bit sequence is used to illustrate this very general but not widely recognized phenomenon. This implies that any predictor with good performance must rely on some (usually implicitly) assumed prior distributions of the problem.

Algorithms↗
PubMed1990

[Intensive care aspects in eclampsia with multiple organ failure].

Because of a good prenatal care eclampsia has been very seldom. But it is still a severe disease. By means of a case report vital symptoms and possible etiologic mechanisms are discussed. The meaning of an interdisciplinary intensive care and a subtle monitoring has been emphasized.

Adult↗
PubMed1989

[Testing with the computer--the Diamed System].

The Diamed System has been developed to reduce the time-consuming testing routines involved in psychopathometric studies of disease course in the field of medicine. Test administration was to be relieved of those activities, in particular in repeat testing, examiners experienced as weary, unpleasant, repetitive, and uncreative. An important aim had been to permit data collection by as independent a dialogue as possible between the patient and the micro-computer, and extremely simple operations and instructions were considered of great importance. The opportunity has, however, also been utilized to implement promising performance testing procedures for measuring basic parameters of mental capability. Beside mental-amnestic capacity, the procedures cover subjective complaints because these, too, frequently are relevant in measuring the course of psychic disorders. The procedures incorporated in the Diamed System permit reliability verifications as to whether self-assessment and independent computerized testing might not be asking too much of the patients intellectually. Most of the procedures will be used for studying disease course in acute Organic Psychosyndromes and in all disorders that are associated with changes in mood and/or with subjective complaints. Diagnostic assistance moreover is offered for determining the presence of acute Organic Psychosyndromes. Under the name of "brain jogging", an economical programme is introduced for mental training, aimed at maintaining and improving basic central information processing capacities. Its effect on intelligence and memory has been demonstrated on in-patient populations, both with and without brain-organic disorders. Notably in the case of acute Organic Psychosyndromes, it has turned out to be an effective supplement to drug treatment.

Arousal↗
PubMed1988

Cross-sectional epidemiological study on neurotoxicity of solvents in paints and lacquers.

In a multi-disciplinary retrospective study we examined 105 house painters employed for at least ten years (median 27 years, range 10-36 years). Fifty-three workers from various professions (non-painters), who were matched with regard to age, occupational training and socio-economic status served as the control group. In both groups no cases of a clinically manifest polyneuropathy or encephalopathy were found. The neurophysiological examinations (EEG and NCV-measurement) showed no differences in painters and controls that would indicate adverse effects of organic solvents. There were no cases with neuroradiological findings of a diffuse cerebral atrophy. Furthermore the evaluation of certain brain structures (ventricular diameter, cella media index) of the CAT films did not reveal any significant differences. In the neurobehavioral tests significant differences in the results were only found in the subtests "change of personality" and "short term memory capacity" in a subgroup of painters with repeated prenarcotic symptoms at the workplace. Ambient air monitoring measurements at 30 representative workplaces showed that the concentrations of the main components of the solvent-mixtures were well below the MAK-values. The results of the "Erlangen Painter Study" does not confirm former epidemiologic findings from other countries, mainly Denmark. However, there are some aspects, such as minor solvent exposure in German house painters, insufficient diagnostic and etiological procedures as well as misclassifications which may explain the different experiences.

Adolescent↗
PubMed1977

[Psychopathometrical results of follow-up studies of trichloroethylene-exposed persons (author's transl)].

Seven clinical healthy volunteers were exposed to trichloroethylene concentration in air with 520 mg/m3 (100 ppm) at an average 6 hours a day on 5 consecutive days. Corresponding volunteers were exposed to a placebo for the same period. --The persons were examined psychopathometrically and biochemically at the beginning and after every day of exposure. The trichloroethylene-metabolites in blood and urine were dated in order to quantify the loads. --Purpose of the psychopathometrical testing methods was the observation, whether a psychological impairment in the sense of a "psychoorganic syndrome" may occur under these exposition-conditions. --Standardized achievement-tests and self-report rating scales were used in order to demonstrate reversible physical provable psychosis that may be possible. Comparing the psychopathometrical results of the exposed and non-exposed volunteers no statistical significant difference was visible in spite of the analytically proved considerable incorporation of the solvent.

Adult↗
PubMed1976

[Short forms of a short psychopathological intelligence test (author's transl)].

Even short tests can still be materially shortened when they are intended to provide rough information. An example of a short intelligence test shows that considerable reductions are permissible when the procedure is intended to classify subjects into IQ groups of roughly "under 100" or "over 100". Also division into three as below average, average and above average level of intelligence is possible, and also division into four grades. If about 85% accuracy is satisfactory, a three-problem test is sufficient. For grading into three and four parts, six and nine problems, respectively may be adequate.

Adult↗