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W Janke

Publications and source records attributed to W Janke.

At least 19 recordsLinked to original sources
PubMed2003

Information geometry of the spherical model.

Motivated by the observation that geometrizing statistical mechanics offers an interesting alternative to more standard approaches, we calculate the scaling behavior of the curvature R of the information geometry metric for the spherical model. We find that R approximately epsilon(-2), where epsilon=beta(c)-beta is the distance from criticality. The discrepancy from the naively expected scaling R approximately epsilon(-3) is explained and compared with that for the Ising model on planar random graphs, which shares the same critical exponents.

Journal Article↗
PubMed2002

Information geometry of the ising model on planar random graphs.

It has been suggested that an information geometric view of statistical mechanics in which a metric is introduced onto the space of parameters provides an interesting alternative characterization of the phase structure, particularly in the case where there are two such parameters, such as the Ising model with inverse temperature beta and external field h. In various two-parameter calculable models, the scalar curvature R of the information metric has been found to diverge at the phase transition point beta(c) and a plausible scaling relation postulated: R approximately |beta-beta(c)|(alpha-2). For spin models the necessity of calculating in nonzero field has limited analytic consideration to one-dimensional, mean-field and Bethe lattice Ising models. In this paper we use the solution in field of the Ising model on an ensemble of planar random graphs (where alpha=-1, beta=1/2, gamma=2) to evaluate the scaling behavior of the scalar curvature, and find R approximately |beta-beta(c)|(-2). The apparent discrepancy is traced back to the effect of a negative alpha.

Journal Article↗
PubMed2001

Softening of first-order transition in three-dimensions by quenched disorder.

We study by extensive Monte Carlo simulations the effect of random bond dilution on the phase transition of the three-dimensional four-state Potts model that is known to exhibit a strong first-order transition in the pure case. The phase diagram in the dilution-temperature plane is determined from the peaks of the susceptibility for sufficiently large system sizes. In the strongly disordered regime, numerical evidence for softening to a second-order transition induced by randomness is given. Here a large-scale finite-size scaling analysis, made difficult due to strong crossover effects presumably caused by the percolation fixed point, is performed.

Journal Article↗
PubMed2001

[Experimental study of the effect of acetylsalicylic acid combined with caffeine regarding possible abuse potential].

Caffeine is suspected to initiate the abuse of caffeine-containing analgesics. To clarify this matter the study investigated the effects of aspirin alone and in combination with caffeine on mood and cardiovascular parameters before, during, and after pain induction through mechanical stimulation. 96 healthy middle-aged women--all habitual coffee drinkers--were randomly designed to receive 0 or 500 mg aspirin together with 0, 50, or 100 mg caffeine administered in a double-blind design. Aspirin did not change ratings of mood scales. Caffeine decreased scores on negative mood scales, especially on the anxiety/sadness scale. The combination of aspirin and caffeine failed to increase any score on scales measuring positive moods. Only a few interactions are noticed. The results do not support the suggestion that caffeine increases the potential for abuse of aspirin.

Adult↗
PubMed1997

Scanning behavior of rats during eating under stressful noise.

Behavioral ecological theories postulate that threatening environments should increase eating speed and vigilance during feeding. In the present experiment, eating speed and scanning behavior during eating were measured in 36 rats in 5 consecutive test sessions under stressful noise (95 dB white noise, n = 18) and control conditions (60 dB, n = 18) after the animals had been habituated to the test environment. Intense noise induced an increase of scanning rate and eating speed. These effects are similar to those reported for novel and light environments.

Animals↗
PubMed1996

Effects of stressful noise on eating and non-eating behavior in rats.

Eating and other behaviors were measured in 36 food-deprived rats on 15 consecutive days during 20 min test sessions. During training sessions 1 to 5 all animals were habituated to the test boxes with white noise of 55 dB intensity. For sessions 6 to 10 noise intensity was increased to 95 dB for the experimental rats and to 60 dB for the control rats. The food intake of experimental rats was lower for stress session 1. The duration of eating behavior was lower, and durations of exploring, grooming and resting behaviors were higher for all stress sessions for rats exposed to 95 dB white noise. Speed of eating behavior was higher for all stress sessions in the experimental group. Defecation rate of the experimental rats was higher for all stress sessions. On post-stress sessions 11 to 15 animals were again tested under the stimulus conditions of the training period (55 dB). No significant effects were observed for this period. The results are discussed with respect to models of "stress-induced" eating and behavioral ecology.

Animals↗
PubMed1995

Experimental models for aggression and inventories for the assessment of aggressive and autoaggressive behavior.

This paper reviews principles realized in questionnaires for the assessment of aggression as well as in experimental models suitable for inducing aggression for the validation of questionnaire scales and for providing experimental models for testing aggression-reducing drug effects. Existing self-rating scales based on factor analysis were shown to measure certain parameters of reactions concerning modes of expression of aggression and its objects. In observer rating scales situations are usually also specified. A final scale containing 9 situations and 17 reactions grouped into seven factors is presented. It could be shown to differentiate between certain types of aggression provoking situations. Furthermore, models suitable for eliciting aggression were developed in three different departments of psychology. They are based on frustration by blockade of goals and critique or subtraction of positive reinforcers ("Tower of Hanoi" and "Superball Game" in Würzburg, "Unsolvable Maze Computer Task" in Berlin) and by a competitive condition combined with application of aversive stimuli by a coplayer ("Modified Buss Machine" in Giessen). All experimental conditions were suitable for inducing anger and emotional arousal, negative ratings of confederates or experimenters, and partly also physiological changes. The results seem promising enough to test the relationship between artificially induced aggression and pathologiocal aggression in further research.

Aggression↗