8 research outputs found
Polymer translocation through a nanopore under an applied external field
We investigate the dynamics of polymer translocation through a nanopore under
an externally applied field using the 2D fluctuating bond model with
single-segment Monte Carlo moves. We concentrate on the influence of the field
strength , length of the chain , and length of the pore on forced
translocation. As our main result, we find a crossover scaling for the
translocation time with the chain length from for
relatively short polymers to for longer chains, where
is the Flory exponent. We demonstrate that this crossover is due to the
change in the dependence of the translocation velocity v on the chain length.
For relatively short chains , which crosses over to for long polymers. The reason for this is that with increasing
there is a high density of segments near the exit of the pore, which slows down
the translocation process due to slow relaxation of the chain. For the case of
a long nanopore for which , the radius of gyration along
the pore, is smaller than the pore length, we find no clear scaling of the
translocation time with the chain length. For large , however, the
asymptotic scaling is recovered. In this regime, is almost independent of . We have previously found that for a polymer,
which is initially placed in the middle of the pore, there is a minimum in the
escape time for . We show here that this minimum
persists for a weak fields such that is less than some critical value,
but vanishes for large values of .Comment: 25 Pages, 10 figures. Submitted to J. Chem. Phys. J. Chem. Phys. 124,
in press (2006
Comment on ``Passage Times for Unbiased Polymer Translocation through a Narrow Pore''
One of the most fundamental quantities associated with polymer translocation
through a nanopore is the translocation time and its dependence on the
chain length . Our simulation results based on both the bond fluctuation
Monte Carlo and Molecular Dynamics methods confirm the original prediction
, which scales in the same manner as the Rouse relaxation
time of the chain except for a larger prefactor, and invalidates other scaling
claims.Comment: 1+pages, 1 Figure, Minor change
Magnetic-Stimulation-Related Physiological Artifacts in Hemodynamic Near-Infrared Spectroscopy Signals
Peer reviewe
Hemodynamic responses to emotional speech in two-month-old infants imaged using diffuse optical tomography
Emotional speech is one of the principal forms of social communication in humans. In this study, we investigated neural processing of emotional speech (happy, angry, sad and neutral) in the left hemisphere of 21 two-month-old infants using diffuse optical tomography. Reconstructed total hemoglobin (HbT) images were analysed using adaptive voxel-based clustering and region-of-interest (ROI) analysis. We found a distributed happy > neutral response within the temporo-parietal cortex, peaking in the anterior temporal cortex; a negative HbT response to emotional speech (the average of the emotional speech conditions angry in the anterior superior temporal sulcus (STS), happy > angry in the superior temporal gyrus and posterior superior temporal sulcus, angry <baseline in the insula, superior temporal sulcus and superior temporal gyrus and happy <baseline in the anterior insula. These results suggest that left STS is more sensitive to happy speech as compared to angry speech, indicating that it might play an important role in processing positive emotions in two-month-old infants. Furthermore, happy speech (relative to neutral) seems to elicit more activation in the temporo-parietal cortex, thereby suggesting enhanced sensitivity of temporo-parietal cortex to positive emotional stimuli at this stage of infant development.Peer reviewe
Hemodynamic Responses to Speech and Music in Newborn Infants
We used near-infrared spectroscopy (NIRS) to study responses to speech and music on the auditory cortices of 13 healthy full-term newborn infants during natural sleep. The purpose of the study was to investigate the lateralization of speech and music responses at this stage of development. NIRS data was recorded from eight positions on both hemispheres simultaneously with electroencephalography, electrooculography, electrocardiography, pulse oximetry, and inclinometry. In 11 subjects, statistically significant (P < 0.02) oxygenated (HbO(2)) and total hemoglobin (HbT) responses were recorded. Both stimulus types elicited significant HbO(2) and HUT responses on both hemispheres in five subjects. Six of the 11 subjects had positive HbO(2) and HbT responses to both stimulus types, whereas one subject had negative responses. Mixed positive and negative responses were observed in four neonates. On both hemispheres, speech and music responses were significantly correlated (r = 0.64; P = 0.018 on the left hemisphere (LH) and r = 0.60; P = 0.029 on the right hemisphere (RH)). On the group level, the average response to the speech stimuli was statistically significantly greater than zero in the LH, whereas responses on the RH or to the music stimuli did not differ significantly from zero. This suggests a more coherent response to speech on the LH. However, significant differences in lateralization of the responses or mean response amplitudes of the two stimulus types were not observed on the group level. Hum Brain Mapp 31:595-603, 2010. (C) 2009 Wiley-Liss, Inc