463 research outputs found
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 () and Ohnesorge
numbers (), defined with the bubble radius . 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 is constant during the collapse
and is shown to be , where is the capillary
velocity and is
the wave resistance factor due to the precursory capillary waves, with
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 in
the equatorial plane, while at the bottom of the cavity
, where
is the static cavity depth. The total volume flux of cavity-filling, which is
entirely contributed by this shrinking, scales as ;
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
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
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)
Deficient sustained attention to response task and P300 characteristics in early Huntington’s disease
Evidence for the extent and nature of attentional impairment in premanifest and manifest Huntington’s disease (HD) is inconsistent. Understanding such impairments may help to better understand early functional changes in HD and could have consequences concerning care for HD patients. We investigated attentional control in both early and premanifest HD. We studied 17 early HD subjects (mean age: 51 years), 12 premanifest HD subjects (mean age: 43 years), and 15 healthy controls (mean age: 51 years), using the sustained attention to response task (SART), a simple Go/No-go test reflecting attentional and inhibitory processes through reaction time (RT) and error rates. Simultaneously recorded EEG yielded P300 amplitudes and latencies. The early HD group made more Go errors (p < 0.001) and reacted slower (p < 0.005) than the other groups. The RT pattern during the SART was remarkably different for early HD subjects compared to the other two groups (p < 0.005), apparent as significant post-error slowing. P300 data showed that for early HD the No-go amplitude was lower than for the other two groups (p < 0.05). Subjects with early HD showed a reduced capacity to effectively control attention. They proved unable to resume the task directly after having made an error, and need more time to return to pre-error performance levels. No attentional control deficits were found for the premanifest HD group
Actionable perturbations of damage responses by TCL1/ATM and epigenetic lesions form the basis of T-PLL
T-cell prolymphocytic leukemia (T-PLL) is a rare and poor-prognostic mature T-cell malignancy. Here we integrated large-scale profiling data of alterations in gene expression, allelic copy number (CN), and nucleotide sequences in 111 well-characterized patients. Besides prominent signatures of T-cell activation and prevalent clonal variants, we also identify novel hot-spots for CN variability, fusion molecules, alternative transcripts, and progression-associated dynamics. The overall lesional spectrum of T-PLL is mainly annotated to axes of DNA damage responses, T-cell receptor/cytokine signaling, and histone modulation. We formulate a multi-dimensional model of T-PLL pathogenesis centered around a unique combination of TCL1 overexpression with damaging ATM aberrations as initiating core lesions. The effects imposed by TCL1 cooperate with compromised ATM toward a leukemogenic phenotype of impaired DNA damage processing. Dysfunctional ATM appears inefficient in alleviating elevated redox burdens and telomere attrition and in evoking a p53-dependent apoptotic response to genotoxic insults. As non-genotoxic strategies, synergistic combinations of p53 reactivators and deacetylase inhibitors reinstate such cell death execution.Peer reviewe
Shifting Attention within Memory Representations Involves Early Visual Areas
Prior studies have shown that spatial attention modulates early visual cortex retinotopically, resulting in enhanced processing of external perceptual representations. However, it is not clear whether the same visual areas are modulated when attention is focused on, and shifted within a working memory representation. In the current fMRI study participants were asked to memorize an array containing four stimuli. After a delay, participants were presented with a verbal cue instructing them to actively maintain the location of one of the stimuli in working memory. Additionally, on a number of trials a second verbal cue instructed participants to switch attention to the location of another stimulus within the memorized representation. Results of the study showed that changes in the BOLD pattern closely followed the locus of attention within the working memory representation. A decrease in BOLD-activity (V1–V3) was observed at ROIs coding a memory location when participants switched away from this location, whereas an increase was observed when participants switched towards this location. Continuous increased activity was obtained at the memorized location when participants did not switch. This study shows that shifting attention within memory representations activates the earliest parts of visual cortex (including V1) in a retinotopic fashion. We conclude that even in the absence of visual stimulation, early visual areas support shifting of attention within memorized representations, similar to when attention is shifted in the outside world. The relationship between visual working memory and visual mental imagery is discussed in light of the current findings
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