Dislocation avalanche correlations

Recently, mechanical tests on ice as well as dislocation dynamics simulations have revealed that plastic flow displays a scale-free intermittent dynamics characterized by dislocation avalanches with a power law distribution of amplitudes. To further explore the complexity of dislocation dynamics during plastic flow, we present a statistical analysis of dislocation avalanche correlations and avalanche triggering. It is shown that the rate of avalanche triggering immediately after any avalanche is larger than the background activity due to uncorrelated events. This self-induced triggering increases in intensity, and remains over the background rate for longer times, as the amplitude of the mainshock increases. This analysis suggests that stress redistributions and the associated collective dislocation rearrangements may be responsible for aftershock triggering in the complex process of plastic deformation.Comment: 8 pages, 3 figures, presented at ICSMA-13, August 2003, Budapes

An Experimental Examination of Cautela\u27s Covert Sensitization as a Smoking Reduction Technique

Experimental studies investigating the aversive imagery technique of Covert Sensitization as a cigarette smoking deterrent have not clearly testified to its effectiveness. They have either deviated from Cautela’s technique and/or confounded their results by adding other components to it. The present study tested the hypothesis that the successful results of Covert Sensitization requires both therapist-administered treatment and instructions that Subjects (Ss) also self-administer treatment. The self-administered treatment (homework) consisted of Ss imagining Covert Sensitization scenes twice a day between meetings with the Experimenter (E). Thirty-six habitual smokers were randomly assigned to one of three training groups; one group of twelve was taught only to imagine Covert Sensitization scenes when described by the E (CSN); a second group of twelve was additionally instructed to practice imagining them tv/ice a day between meetings (CSH); a third group of twelve was taught to relax using Wolpe’s relaxation technique and told to practice relaxing twice a day between meetings (RH). The three E\u27s, who were randomly assigned one group from each condition, trained each of the thirty-six Ss, and collected self-report data during six hourly sessions and four follow-up weeks. Analysis of the data indicated that the groups smoked at different rates over time, and that the RH group smoked less than the C3N group over the follow-up periods. Although all the groups smoked fev/er cigarettes once treatment began, the GSN group then increased its smoking rate throughout both treatment and follow-up weeks and the CSH group increased its smoking once treatment stopped. However, contrary to expectations, the RH group generally continued its decrease toward zero cigarettes smoked. Speculation about these results and implications for future research were discussed, and it was suggested that the Covert Sensitization treatment was ineffective because of a low frequency of punishment or the possible use of weak aversive scenes by the Es. The effectiveness of the RH treatment was interpreted as due to its dealing with tension, a possible underlying cause of smoking. The reader was cautioned that these results may have been influenced by uncontrolled factors and ways to deal with these factors in future studies were discussed. Although the results of this study were inconclusive, this study has opened further areas for investigation

Examination of Some Variables in Relation to Perceived Locus of Control

Several studies indicate that the Internal Locus of Control Scale (Rotter, 1962) may also be an indicator of concern or anxiety. The present study was designed to assess whether IE and task variable manipulation would be reflected in physiological and decision time measurements. The specific dependent variables chosen were blood pressure, pulse rate, respiration rate and decision time. Past evidence suggests that E\u27s are more anxious than I’s, and that anxiety is reflected by a decrease in blood pressure. Evidence also points to the possibility that the other dependent variables considered are affected by IE and task manipulation, although not necessarily in a manner correlated with blood pressure. Each of sixty internal and external subjects served as their own controls by participating in both a skill and a chance task at the same sitting. All measurements were recorded by a commercial four channel polygraph. A 2x2x2 design was used, with two types of subjects (internal and external), two types of tasks (chance and skill), and two levels of order (skill first, chance first). Analysis of the data indicated that the respiration rate of the internals was greater than that of the externals and the blood pressure of the internal group participating in a chance task was greater than that of the internal group participating in a skill task

Complexity in dislocation dynamics: model

We propose a numerical model to study the viscoplastic deformation of ice single crystals. We consider long-range elastic interactions among dislocations, the possibility of mutual annihilation, and a multiplication mechanism representing the activation of Frank-Read sources due to dislocation pinning. The overdamped equations of motion for a collection of dislocations are integrated numerically using different externally applied stresses. Using this approach we analyze the avalanche-like rearrangements of dislocations during the dynamic evolution. We observe a power law distribution of avalanche sizes which we compare with acoustic emission experiments in ice single crystals under creep deformation. We emphasize the connections of our model with non-equilibrium phase transitions and critical phenomena

Scaling analysis of deformation field within granular materials: application to strain localization

Discrete element method (DEM) simulations using periodic boundary conditions and molecular dynamics are conducted on a frictional granular media. Two dimensional strain controlled biaxial tests are carried out on an assembly of circular particles interacting via elastic contacts and Coulomb friction. The spatial correlations that take place within the deformation field along the loading path are tracked by a scaling analysis of the continuous strain rate field. This method allows us to discuss the degree of strain localization occurring throughout the test. The analysis of the correlation length in the early stages of macroscopic deformation leads to the identification of two distinct behaviors. First, a divergence of the correlation length on the first deformation invariant, i.e. the divergence, is reported at the onset of macroscopic dilation. This suggests an interpretation of the contraction peak as a critical point. Secondly, an increase of the correlation length on the second deformation invariant, i.e. the shear, is also observed before the peak load. However, saturation remains on the scaling law. We argue that this second behavior is associated to macroscopic shear banding: our analysis accurately gives its outbreak on the stress versus strain curve. Finally, a dependence of the correlation length as a function of the deformation window considered is reported. This shows that scaling properties within the deformation field emerge from long range interactions within an assembly of rigid frictional particles

Bimodal coupling of ripples and slower oscillations during sleep in patients with focal epilepsy.

OBJECTIVE: Differentiating pathologic and physiologic high-frequency oscillations (HFOs) is challenging. In patients with focal epilepsy, HFOs occur during the transitional periods between the up and down state of slow waves. The preferred phase angles of this form of phase-event amplitude coupling are bimodally distributed, and the ripples (80-150 Hz) that occur during the up-down transition more often occur in the seizure-onset zone (SOZ). We investigated if bimodal ripple coupling was also evident for faster sleep oscillations, and could identify the SOZ. METHODS: Using an automated ripple detector, we identified ripple events in 40-60 min intracranial electroencephalography (iEEG) recordings from 23 patients with medically refractory mesial temporal lobe or neocortical epilepsy. The detector quantified epochs of sleep oscillations and computed instantaneous phase. We utilized a ripple phasor transform, ripple-triggered averaging, and circular statistics to investigate phase event-amplitude coupling. RESULTS: We found that at some individual recording sites, ripple event amplitude was coupled with the sleep oscillatory phase and the preferred phase angles exhibited two distinct clusters (p \u3c 0.05). The distribution of the pooled mean preferred phase angle, defined by combining the means from each cluster at each individual recording site, also exhibited two distinct clusters (p \u3c 0.05). Based on the range of preferred phase angles defined by these two clusters, we partitioned each ripple event at each recording site into two groups: depth iEEG peak-trough and trough-peak. The mean ripple rates of the two groups in the SOZ and non-SOZ (NSOZ) were compared. We found that in the frontal (spindle, p = 0.009; theta, p = 0.006, slow, p = 0.004) and parietal lobe (theta, p = 0.007, delta, p = 0.002, slow, p = 0.001) the SOZ incidence rate for the ripples occurring during the trough-peak transition was significantly increased. SIGNIFICANCE: Phase-event amplitude coupling between ripples and sleep oscillations may be useful to distinguish pathologic and physiologic events in patients with frontal and parietal SOZ

Preservation and detectability of shock-induced magnetization

An understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites, lunar rocks, and cratered planetary surfaces. Rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization (SRM) due to the passage of a shock wave in the presence of an ambient magnetic field. In this study, we conducted pressure remanent magnetization (PRM) acquisition experiments on a variety of natural samples as an analog for SRM acquisition at pressures ranging up to 1.8 GPa. Comparison of the alternating field (AF) and thermal demagnetization behavior of PRM confirms that AF demagnetization is a more efficient method for removing SRM overprints than thermal demagnetization because SRM may persist to unblocking temperatures approaching the Curie temperatures of magnetic minerals. The blocking of SRM to high temperatures suggests that SRM could persist without being eradicated by viscous relaxation over geologic timescales. However, SRM has been rarely observed in natural samples likely because of two factors: (1) other forms of impact-related remanence (e.g., thermal remanent magnetization from impact-related heating or chemical remanent magnetization from postimpact hydrothermal activity) are often acquired by target rocks that overprint SRM, and (2) low SRM acquisition efficiencies may prevent SRM from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity