45,649 research outputs found
Literacy: A cultural influence on functional left-right differences in the inferior parietal cortex
The current understanding of hemispheric interaction is limited. Functional hemispheric specialization is likely to depend on both genetic and environmental factors. In the present study we investigated the importance of one factor, literacy, for the functional lateralization in the inferior parietal cortex in two independent samples of literate and illiterate subjects. The results show that the illiterate group are consistently more right-lateralized than their literate controls. In contrast, the two groups showed a similar degree of left-right differences in early speech-related regions of the superior temporal cortex. These results provide evidence suggesting that a cultural factor, literacy, influences the functional hemispheric balance in reading and verbal working memory-related regions. In a third sample, we investigated grey and white matter with voxel-based morphometry. The results showed differences between literacy groups in white matter intensities related to the mid-body region of the corpus callosum and the inferior parietal and parietotemporal regions (literate > illiterate). There were no corresponding differences in the grey matter. This suggests that the influence of literacy on brain structure related to reading and verbal working memory is affecting large-scale brain connectivity more than grey matter per se
Entanglement of two-qubit photon beam by magnetic field
We have studied the possibility of affecting the entanglement measure of
2-qubit system consisting of two photons with different fixed frequencies but
with two arbitrary linear polarizations, moving in the same direction, by the
help of an applied external magnetic field. The interaction between the
magnetic field and the photons in our model is achieved through intermediate
electrons that interact with both the photons and the magnetic field. The
possibility of exact theoretical analysis of this scheme is based on known
exact solutions that describe the interaction of an electron subjected to an
external magnetic field (or a medium of electrons not interacting with each
other) with a quantized field of two photons. We adapt these exact solutions to
the case under consideration. Using explicit wave functions for the resulting
electromagnetic field, we calculate the entanglement measure of the photon beam
as a function of the applied magnetic field and parameters of the electron
medium
Cabibbo-suppressed non-leptonic B- and D-decays involving tensor mesons
The Cabibbo-suppressed non-leptonic decays of B (and D) mesons to final
states involving tensor mesons are computed using the non-relativistic quark
model of Isgur-Scora-Grinstein-Wise with the factorization hypothesis. We find
that some of these B decay modes, as B --> (K^*, D^*)D^*_2, can have branching
ratios as large as 6 x 10^{-5} which seems to be at the reach of future B
factories.Comment: Latex, 11 pages, to appear in Phys. Rev.
Pseudospectral versus finite-differences schemes in the numerical integration of stochastic models of surface growth
We present a comparison between finite differences schemes and a
pseudospectral method applied to the numerical integration of stochastic
partial differential equations that model surface growth. We have studied, in
1+1 dimensions, the Kardar, Parisi and Zhang model (KPZ) and the Lai, Das Sarma
and Villain model (LDV). The pseudospectral method appears to be the most
stable for a given time step for both models. This means that the time up to
which we can follow the temporal evolution of a given system is larger for the
pseudospectral method. Moreover, for the KPZ model, a pseudospectral scheme
gives results closer to the predictions of the continuum model than those
obtained through finite difference methods. On the other hand, some numerical
instabilities appearing with finite difference methods for the LDV model are
absent when a pseudospectral integration is performed. These numerical
instabilities give rise to an approximate multiscaling observed in the
numerical simulations. With the pseudospectral approach no multiscaling is seen
in agreement with the continuum model.Comment: 13 single column pages, RevTeX, 6 eps fig
Higher particle form factors of branch point twist fields in integrable quantum field theories
In this paper we compute higher particle form factors of branch point twist
fields. These fields were first described in the context of massive
1+1-dimensional integrable quantum field theories and their correlation
functions are related to the bi-partite entanglement entropy. We find analytic
expressions for some form factors and check those expressions for consistency,
mainly by evaluating the conformal dimension of the corresponding twist field
in the underlying conformal field theory. We find that solutions to the form
factor equations are not unique so that various techniques need to be used to
identify those corresponding to the branch point twist field we are interested
in. The models for which we carry out our study are characterized by staircase
patterns of various physical quantities as functions of the energy scale. As
the latter is varied, the beta-function associated to these theories comes
close to vanishing at several points between the deep infrared and deep
ultraviolet regimes. In other words, renormalisation group flows approach the
vicinity of various critical points before ultimately reaching the ultraviolet
fixed point. This feature provides an optimal way of checking the consistency
of higher particle form factor solutions, as the changes on the conformal
dimension of the twist field at various energy scales can only be accounted for
by considering higher particle form factor contributions to the expansion of
certain correlation functions.Comment: 25 pages, 4 figures; v2 contains small correction
Graphene as an electronic membrane
Experiments are finally revealing intricate facts about graphene which go
beyond the ideal picture of relativistic Dirac fermions in pristine two
dimensional (2D) space, two years after its first isolation. While observations
of rippling added another dimension to the richness of the physics of graphene,
scanning single electron transistor images displayed prevalent charge
inhomogeneity. The importance of understanding these non-ideal aspects cannot
be overstated both from the fundamental research interest since graphene is a
unique arena for their interplay, and from the device applications interest
since the quality control is a key to applications. We investigate the membrane
aspect of graphene and its impact on the electronic properties. We show that
curvature generates spatially varying electrochemical potential. Further we
show that the charge inhomogeneity in turn stabilizes ripple formation.Comment: 6 pages, 11 figures. Updated version with new results about the
re-hybridization of the electronic orbitals due to rippling of the graphene
sheet. The re-hybridization adds the next-to-nearest neighbor hopping effect
discussed in the previous version. New reference to recent STM experiments
that give support to our theor
Dynamics of quantum correlations and linear entropy in a multi-qubit-cavity system
We present a theoretical study of the relationship between entanglement and
entropy in multi-qubit quantum optical systems. Specifically we investigate
quantitative relations between the concurrence and linear entropy for a
two-qubit mixed system, implemented as two two-level atoms interacting with a
single-mode cavity field. The dynamical evolutions of the entanglement and
entropy, are controlled via time-dependent cavity-atom couplings. Our
theoretical findings lead us to propose an alternative measure of entanglement,
which could be used to develop a much needed correlation measure for more
general multi-partite quantum systems.Comment: New discussions on the generality of entanglement-entropy
relationship, one new reference, and other minor changes. 10 pages, 6
figures, accepted for publication in J.Opt. B: "Special Issue on Fluctuations
& Noise in Photonics & Quantum Optics.
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