Dynamics of collapse of free-surface bubbles: effects of gravity and viscosity

The rupture of the thin film at the top of a bubble floating at a liquid-gas interface leads to the axisymmetric collapse of the bubble cavity. We present scaling laws for such a cavity collapse, established from experiments conducted with bubbles spanning a wide range of Bond (${10^{-3}<Bo\leq1}$) and Ohnesorge numbers (${10^{-3}<Oh<10^{-1}}$), defined with the bubble radius $R$. The cavity collapse is a capillary-driven process, with a dependency on viscosity and gravity affecting, respectively, precursory capillary waves on the cavity boundary, and the static bubble shape. The collapse is characterised by tangential and normal velocities of the kink, formed by the intersection of the concave cavity opening after the top thin film rupture, with the convex bubble cavity boundary. The tangential velocity $U_t$ is constant during the collapse and is shown to be $U_t=4.5~U_c{\mathcal{W}}_R$, where $U_c$ is the capillary velocity and ${\mathcal{W}}_R(Oh,Bo)={(1-\sqrt{Oh {\mathscr{L}}} )^{-1/2}}$ is the wave resistance factor due to the precursory capillary waves, with $\mathscr{L}(Bo)$ being the path correction of the kink motion. The movement of the kink in the normal direction is part of the inward shrinkage of the whole cavity due to the sudden reduction of gas pressure inside the bubble cavity after the thin film rupture. This normal velocity is shown to scale as $U_c$ in the equatorial plane, while at the bottom of the cavity $\overline{U}_{nb}=U_c(Z_c/R)({\mathcal{W}_R}/ {\mathscr{L}})$, where $Z_c(Bo)$ is the static cavity depth. The total volume flux of cavity-filling, which is entirely contributed by this shrinking, scales as ${Q_T\simeq 2\pi R Z_c U_c}$; remains a constant throughout the collapse.Comment: 22 page

3-D Perturbations in Conformal Turbulence

The effects of three-dimensional perturbations in two-dimensional turbulence are investigated, through a conformal field theory approach. We compute scaling exponents for the energy spectra of enstrophy and energy cascades, in a strong coupling limit, and compare them to the values found in recent experiments. The extension of unperturbed conformal turbulence to the present situation is performed by means of a simple physical picture in which the existence of small scale random forces is closely related to deviations of the exact two-dimensional fluid motion.Comment: Discussion of intermittency improved. Figure include

Electrophysiological evidence of alcohol-related attentional bias in social drinkers low in alcohol sensitivity.

Low sensitivity (LS) to the acute effects of alcohol is a known risk-factor for alcoholism. However, little is known concerning potential information-processing routes by which this risk factor might contribute to increased drinking. We tested the hypothesis that LS participants would show biased attention to alcohol cues, compared to their high-sensitivity (HS) counterparts. Participants performed a task in which alcoholic and nonalcoholic beverage cues were presented bilaterally followed by a target that required categorization by color. Response times were faster for targets appearing in alcohol-cued than nonalcohol-cued locations for LS but not for HS participants. Event-related potential markers of early attention orienting (P1 amplitude) and subsequent attention reorienting (ipsilateral invalid negativity [IIN] amplitude) indicated preferential selective attention to alcohol-cued locations among LS individuals. Controlling for recent drinking and family history of alcoholism did not affect these patterns, except that among HS participants relatively heavy recent drinking was associated with difficulty reorienting attention away from alcohol-cued locations. These findings suggest a potential information-processing bias through which low sensitivity could lead to heavy alcohol involvement

Numbers in the Blind's “Eye”

Background: Although lacking visual experience with numerosities, recent evidence shows that the blind perform similarly to sighted persons on numerical comparison or parity judgement tasks. In particular, on tasks presented in the auditory modality, the blind surprisingly show the same effect that appears in sighted persons, demonstrating that numbers are represented through a spatial code, i.e. the Spatial-Numerical Association of Response Codes (SNARC) effect. But, if this is the case, how is this numerical spatial representation processed in the brain of the blind? Principal Findings: Here we report that, although blind and sighted people have similarly organized numerical representations, the attentional shifts generated by numbers have different electrophysiological correlates (sensorial N100 in the sighted and cognitive P300 in the blind). Conclusions: These results highlight possible differences in the use of spatial representations acquired through modalities other than vision in the blind population

From learned value to sustained bias: how reward conditioning changes attentional priority

Attentional bias to reward-associated stimuli can occur even when it interferes with goal-driven behavior. One theory posits that striatal activitydopaminergic siganaling in the striatum during reward conditioning leads to changes in visual cortical and parietal representations of the stimulus used; this in turn sustains attentional bias even when reward is discontinued. However, only a few studies have examined neural activity during both rewarded and unrewarded task phases. In the current study, participants first completed a reward-conditioned conditioning learning phase, during which responses to certain stimuli were associated with monetary reward. These stimuli were then included as non-predictive cues in a spatial cueing task. Participants underwent functional brain imaging during both task phases. Results show that striatal activity during the learning phase predicted increased visual cortical and parietal activity, and decreased ventro-medial prefrontal cortex activity, in response to conditioned stimuli at test. Striatal activity was also associated with anterior cingulate cortex activation when the reward-conditioned stimulus directed attention away from the target. Our findings Findings suggest that striatal activity during reward conditioning predicts the degree to which reward history biases attention through learning-induced changes in visual and parietal activity

Reinstated p53 response and high anti-T-cell leukemia activity by the novel alkylating deacetylase inhibitor tinostamustine

Non peer reviewe

Attentive Learning of Sequential Handwriting Movements: A Neural Network Model

Defense Advanced research Projects Agency and the Office of Naval Research (N00014-95-1-0409, N00014-92-J-1309); National Science Foundation (IRI-97-20333); National Institutes of Health (I-R29-DC02952-01)