306 research outputs found
Is the whole really more than the sum of its parts? Estimates of average size and orientation are susceptible to object substitution masking
We have a remarkable ability to accurately estimate average featural information across groups of objects, such as their average size or orientation. It has been suggested that, unlike individual object processing, this process of feature averaging occurs automatically and relatively early in the course of perceptual processing, without the need for objects to be processed to the same extent as is required for individual object identification. Here, we probed the processing stages involved in feature averaging by examining whether feature averaging is resistant to object substitution masking (OSM). Participants estimated the average size (Experiment 1) or average orientation (Experiment 2) of groups of briefly presented objects. Masking a subset of the objects using OSM reduced the extent to which these objects contributed to estimates of both average size and average orientation. Contrary to previous findings, these results suggest that feature averaging benefits from late stages of processing, subsequent to the initial registration of featural information
Excitons in narrow-gap carbon nanotubes
We calculate the exciton binding energy in single-walled carbon nanotubes
with narrow band gaps, accounting for the quasi-relativistic dispersion of
electrons and holes. Exact analytical solutions of the quantum relativistic
two-body problem are obtain for several limiting cases. We show that the
binding energy scales with the band gap, and conclude on the basis of the data
available for semiconductor nanotubes that there is no transition to an
excitonic insulator in quasi-metallic nanotubes and that their THz applications
are feasible.Comment: 11 pages, 3 figures. Several references and an additional appendix
adde
Parietal disruption alters audiovisual binding in the sound-induced flash illusion
Selective attention and multisensory integration are fundamental to perception, but little is known about whether, or under what circumstances, these processes interact to shape conscious awareness. Here, we used transcranial magnetic stimulation (TMS) to investigate the causal role of attention-related brain networks in multisensory integration between visual and auditory stimuli in the sound-induced flash illusion. The flash illusion is a widely studied multisensory phenomenon in which a single flash of light is falsely perceived as multiple flashes in the presence of irrelevant sounds. We investigated the hypothesis that extrastriate regions involved in selective attention, specifically within the right parietal cortex, exert an influence on the multisensory integrative processes that cause the flash illusion. We found that disruption of the right angular gyrus, but not of the adjacent supramarginal gyrus or of a sensory control site, enhanced participants' veridical perception of the multisensory events, thereby reducing their susceptibility to the illusion. Our findings suggest that the same parietal networks that normally act to enhance perception of attended events also play a role in the binding of auditory and visual stimuli in the sound-induced flash illusion
Explicit and Exact Solutions to a Kolmogorov-Petrovskii-Piskunov Equation
Some explicit traveling wave solutions to a Kolmogorov-Petrovskii-Piskunov
equation are presented through two ans\"atze. By a Cole-Hopf transformation,
this Kolmogorov-Petrovskii-Piskunov equation is also written as a bilinear
equation and further two solutions to describe nonlinear interaction of
traveling waves are generated. B\"acklund transformations of the linear form
and some special cases are considered.Comment: 14pages, Latex, to appear in Intern. J. Nonlinear Mechanics, the
original latex file is not complet
Classical Integrable 2-dim Models Inspired by SUSY Quantum Mechanics
A class of integrable 2-dim classical systems with integrals of motion of
fourth order in momenta is obtained from the quantum analogues with the help of
deformed SUSY algebra. With similar technique a new class of potentials
connected with Lax method is found which provides the integrability of
corresponding 2-dim hamiltonian systems. In addition, some integrable 2-dim
systems with potentials expressed in elliptic functions are explored.Comment: 19 pages, LaTeX, final version to be published in J.Phys.
Classical Noncommutative Electrodynamics with External Source
In a -noncommutative (NC) gauge field theory we extend the
Seiberg-Witten (SW) map to include the (gauge-invariance-violating) external
current and formulate - to the first order in the NC parameter -
gauge-covariant classical field equations. We find solutions to these equations
in the vacuum and in an external magnetic field, when the 4-current is a static
electric charge of a finite size , restricted from below by the elementary
length. We impose extra boundary conditions, which we use to rule out all
singularities, included, from the solutions. The static charge proves to
be a magnetic dipole, with its magnetic moment being inversely proportional to
its size . The external magnetic field modifies the long-range Coulomb field
and some electromagnetic form-factors. We also analyze the ambiguity in the SW
map and show that at least to the order studied here it is equivalent to the
ambiguity of adding a homogeneous solution to the current-conservation
equation
Green's function for a Schroedinger operator and some related summation formulas
Summation formulas are obtained for products of associated Lagurre
polynomials by means of the Green's function K for the Hamiltonian H =
-{d^2\over dx^2} + x^2 + Ax^{-2}, A > 0. K is constructed by an application of
a Mercer type theorem that arises in connection with integral equations. The
new approach introduced in this paper may be useful for the construction of
wider classes of generating function.Comment: 14 page
On the complete analytic structure of the massive gravitino propagator in four-dimensional de Sitter space
With the help of the general theory of the Heun equation, this paper
completes previous work by the authors and other groups on the explicit
representation of the massive gravitino propagator in four-dimensional de
Sitter space. As a result of our original contribution, all weight functions
which multiply the geometric invariants in the gravitino propagator are
expressed through Heun functions, and the resulting plots are displayed and
discussed after resorting to a suitable truncation in the series expansion of
the Heun function. It turns out that there exist two ranges of values of the
independent variable in which the weight functions can be divided into
dominating and sub-dominating family.Comment: 21 pages, 9 figures. The presentation has been further improve
Statistics of Rare Events in Disordered Conductors
Asymptotic behavior of distribution functions of local quantities in
disordered conductors is studied in the weak disorder limit by means of an
optimal fluctuation method. It is argued that this method is more appropriate
for the study of seldom occurring events than the approaches based on nonlinear
-models because it is capable of correctly handling fluctuations of the
random potential with large amplitude as well as the short-scale structure of
the corresponding solutions of the Schr\"{o}dinger equation. For two- and
three-dimensional conductors new asymptotics of the distribution functions are
obtained which in some cases differ significantly from previously established
results.Comment: 17 pages, REVTeX 3.0 and 1 Postscript figur
Statistics of anomalously localized states at the center of band E=0 in the one-dimensional Anderson localization model
We consider the distribution function of the eigenfunction
amplitude at the center-of-band (E=0) anomaly in the one-dimensional
tight-binding chain with weak uncorrelated on-site disorder (the
one-dimensional Anderson model). The special emphasis is on the probability of
the anomalously localized states (ALS) with much larger than the
inverse typical localization length . Using the solution to the
generating function found recently in our works we find the
ALS probability distribution at . As
an auxiliary preliminary step we found the asymptotic form of the generating
function at which can be used to compute other
statistical properties at the center-of-band anomaly. We show that at
moderately large values of , the probability of ALS at E=0
is smaller than at energies away from the anomaly. However, at very large
values of , the tendency is inverted: it is exponentially
easier to create a very strongly localized state at E=0 than at energies away
from the anomaly. We also found the leading term in the behavior of
at small and show that it is
consistent with the exponential localization corresponding to the Lyapunov
exponent found earlier by Kappus and Wegner and Derrida and Gardner.Comment: 25 pages, 9 figure
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