402 research outputs found
Coherent control of enrichment and conversion of molecular spin isomers
A theoretical model of nuclear spin conversion in molecules controlled by an
external electromagnetic radiation resonant to rotational transition has been
developed. It has been shown that one can produce an enrichment of spin isomers
and influence their conversion rates in two ways, through coherences and
through level population change induced by radiation. Influence of conversion
is ranged from significant speed up to almost complete inhibition of the
process by proper choice of frequency and intensity of the external field.Comment: REVTEX, 13 pages + 6 eps figure
Gesture's body orientation modulates the N400 for visual sentences primed by gestures
Body orientation of gesture entails socialâcommunicative intention, and may thus influence how gestures are perceived and comprehended together with auditory speech during faceâtoâface communication. To date, despite the emergence of neuroscientific literature on the role of body orientation on hand action perception, limited studies have directly investigated the role of body orientation in the interaction between gesture and language. To address this research question, we carried out an electroencephalography (EEG) experiment presenting to participants (n = 21) videos of frontal and lateral communicative hand gestures of 5 s (e.g., raising a hand), followed by visually presented sentences that are either congruent or incongruent with the gesture (e.g., âthe mountain is high/lowâŠâ). Participants underwent a semantic probe task, judging whether a target word is related or unrelated to the gestureâsentence event. EEG results suggest that, during the perception phase of handgestures, while both frontal and lateral gestures elicited a power decrease in both the alpha (8â12âHz) and the beta (16â24âHz) bands, lateral versus frontal gestures elicited reduced power decrease in the beta band, sourceâlocated to the medial prefrontal cortex. For sentence comprehension, at the critical word whose meaning is congruent/incongruent with the gesture prime, frontal gestures elicited an N400 effect for gestureâsentence incongruency. More importantly, this incongruency effect was significantly reduced for lateral gestures. These findings suggest that body orientation plays an important role in gesture perception, and that its inferred socialâcommunicative intention may influence gestureâlanguage interaction at semantic level
Antagonism between brain regions relevant for cognitive control and emotional memory facilitates the generation of humorous ideas
The ability to generate humor gives rise to positive emotions and thus facilitate the successful resolution of adversity. Although there is consensus that inhibitory processes might be related to broaden the way of thinking, the neural underpinnings of these mechanisms are largely unknown. Here, we use functional Magnetic Resonance Imaging, a humorous alternative uses task and a stroop task, to investigate the brain mechanisms underlying the emergence of humorous ideas in 24 subjects. Neuroimaging results indicate that greater cognitive control abilities are associated with increased activation in the amygdala, the hippocampus and the superior and medial frontal gyrus during the generation of humorous ideas. Examining the neural mechanisms more closely shows that the hypoactivation of frontal brain regions is associated with an hyperactivation in the amygdala and vice versa. This antagonistic connectivity is concurrently linked with an increased number of humorous ideas and enhanced amygdala responses during the task. Our data therefore suggests that a neural antagonism previously related to the emergence and regulation of negative affective responses, is linked with the generation of emotionally positive ideas and may represent an important neural pathway supporting mental health
Theory of nuclear spin conversion in ethylene
First theoretical analysis of the nuclear spin conversion in ethylene
molecules (13^CCH4) has been performed. The conversion rate was found equal
approx. 3x10^{-4} 1/s*Torr, which is in qualitative agreement with the recently
obtained experimental value. It was shown that the ortho-para mixing in 13^CCH4
is dominated by the spin-rotation coupling. Mixing of only two pairs of
ortho-para levels were found to contribute significantly to the spin
conversion.Comment: 20 pages, 5 eps figure
Lambda-proton correlations in relativistic heavy ion collisions
The prospect of using lambda-proton correlations to extract source sizes in
relativistic heavy ion collisions is investigated. It is found that the strong
interaction induces a large peak in the correlation function that provides more
sensitive source size measurements than two-proton correlations under some
circumstances. The prospect of using lambda-proton correlations to measure the
time lag between lambda and proton emissions is also studied.Comment: 4 pages, 3 figure, revtex style. Two short paragraphs are added at
referees' recommendations. Phys. Rev. Lett. in pres
The Lambda-Lambda Interaction and ^{6}_{Lambda Lambda}He
An OBE potential model for the ^{1}S_0 S = -2 interaction is analyzed with
emphasis on the role of coupling between the Lambda Lambda, N Xi, and Sigma
Sigma channels. Singlet scalar exchange, an approximation to two-pion exchange,
is significant in all channels; surprisingly, the one-pion exchange component
is almost negligible. The size of the channel coupling as a function of the
overall strength of the OBE model potential is examined. Implications of the
analysis for the binding energy of ^{6}_{Lambda Lambda}He are considered; the
new experimental datum may suggest a consistency between the extracted Lambda
Lambda matrix element and the relation implied by SU(3) among OBE baryon-baryon
interactions. \\Comment: 4 pages brief report to Physical Review
On spin-rotation contribution to nuclear spin conversion in C_{3v}-symmetry molecules. Application to CH_3F
The symmetrized contribution of E-type spin-rotation interaction to
conversion between spin modifications of E- and A_1-types in molecules with
C_{3v}-symmetry is considered. Using the high-J descending of collisional
broadening for accidental rotational resonances between these spin
modifications, it was possible to co-ordinate the theoretical description of
the conversion with (updated) experimental data for two carbon-substituted
isotopes of fluoromethane. As a result, both E-type spin-rotation constants are
obtained. They are roughly one and a half times more than the corresponding
constants for (deutero)methane.Comment: 13 pages with single-spacing, REVTeX, no figures, accepted for
publication in <J. Phys. B
Nucleon-Nucleon Scattering from Effective Field Theory
We perform a nonperturbative calculation of the 1S0 NN scattering amplitude
using an effective field theory (EFT) expansion. The expansion we advocate is a
modification of what has been used previously; it is no a chiral expansion in
powers of the pion mass. We use dimensional regularization throughout and the
MS-bar subtraction scheme; our final result depends only on physical
observables. We show that the EFT expansion of the quantity |p|cot delta(p)
converges at momenta much greater than the scale that characterizes the
derivative expansion of the EFT Lagrangian. Our conclusions are optimistic
about the applicability of an EFT approach to the quantitative study of nuclear
matter.Comment: Revised discussion of power counting in the EFT expansion. Tex file
uses harvmac, epsf macros, 35 pages with 9 postscript figure
Diffusion in disordered systems under iterative measurement
We consider a sequence of idealized measurements of time-separation onto a discrete one-dimensional disordered system. A connection with Markov
chains is found. For a rapid sequence of measurements, a diffusive regime
occurs and the diffusion coefficient is analytically calculated. In a
general point of view, this result suggests the possibility to break the
Anderson localization due to decoherence effects. Quantum Zeno effect emerges
because the diffusion coefficient vanishes at the limit .Comment: 8 pages, 0 figures, LATEX. accepted in Phys.Rev.
- âŠ