119,281 research outputs found
Long-range coupling of prefrontal cortex and visual (MT) or polysensory (STP) cortical areas in motion perception
To investigate how, where and when moving
auditory cues interact with the perception of object-motion
during self-motion, we conducted psychophysical, MEG, and
fMRI experiments in which the subjects viewed nine textured
objects during simulated forward self-motion. On each trial,
one object was randomly assigned its own looming motion
within the scene. Subjects reported which of four labeled objects
had independent motion within the scene in two conditions:
(1) visual information only and (2) with additional moving-
auditory cue.
In MEG, comparison of the two conditions showed: (i) MT
activity is similar across conditions, (ii) late after the stimulus
presentation there is additional activity in the auditory cue
condition ventral to MT, (iii) with the auditory cue, the right
auditory cortex (AC) shows early activity together with STS,
(iv) these two activities have different time courses and the
STS signals occur later in the epoch together with frontal
activity in the right hemisphere, (v) for the visual-only condition
activity in PPC (posterior parietal cortex) is stronger than
in the auditory-cue condition. fMRI conducted for visual-only
condition reveals activations in a network of parietal and frontal
areas and in MT.
In addition, Dynamic Granger Causality analysis showed
for auditory cues a strong connection of the AC with STP but
not with MT suggesting binding of visual and auditory information
at STP. Also, while in the visual-only condition PFC is
connected with MT, in the auditory-cue condition PFC is connected
to STP (superior temporal polysensory) area.
These results indicate that PFC allocates attention to the
“object” as a whole, in STP to a moving visual-auditory object,
and in MT to a moving visual object.Accepted manuscrip
An experimental study of a self-confined flow with ring-vorticity distribution
A new form of self-confined flow was investigated in which a recirculation zone forms away from any solid boundary. An inviscid flow analysis indicated that in a purely meridional axisymmetric flow a stationary, spherical, self-confined region should occur in the center of a streamlined divergent-convergent enlargement zone. The spherical confinement region would be at rest and at constant pressure. Experimental investigations were carried out in a specially built test apparatus to establish the desired confined flow. The streamlined divergent-convergent interior shape of the test section was fabricated according to the theoretical calculation for a particular streamline. The required inlet vorticity distribution was generated by producing a velocity profile with a shaped gauze screen in the straight pipe upstream of the test section. Fluid speed and turbulence intensity were measured with a constant-temperature hot-wire anemometer system. The measured results indicated a very orderly and stable flow field
Thermodynamical Consistent Modeling and Analysis of Nematic Liquid Crystal Flows
The general Ericksen-Leslie system for the flow of nematic liquid crystals is
reconsidered in the non-isothermal case aiming for thermodynamically consistent
models. The non-isothermal model is then investigated analytically. A fairly
complete dynamic theory is developed by analyzing these systems as quasilinear
parabolic evolution equations in an -setting. First, the existence of
a unique, local strong solution is proved. It is then shown that this solution
extends to a global strong solution provided the initial data are close to an
equilibrium or the solution is eventually bounded in the natural norm of the
underlying state space. In these cases, the solution converges exponentially to
an equilibrium in the natural state manifold
Towards Long-endurance Flight: Design and Implementation of a Variable-pitch Gasoline-engine Quadrotor
Majority of today's fixed-pitch, electric-power quadrotors have short flight
endurance ( 1 hour) which greatly limits their applications. This paper
presents a design methodology for the construction of a long-endurance
quadrotor using variable-pitch rotors and a gasoline-engine. The methodology
consists of three aspects. Firstly, the rotor blades and gasoline engine are
selected as a pair, so that sufficient lift can be comfortably provided by the
engine. Secondly, drivetrain and airframe are designed. Major challenges
include airframe vibration minimization and power transmission from one engine
to four rotors while keeping alternate rotors contra-rotating. Lastly, a PD
controller is tuned to facilitate preliminary flight tests. The methodology has
been verified by the construction and successful flight of our gasoline
quadrotor prototype, which is designed to have a flight time of 2 to 3 hours
and a maximum take-off weight of 10 kg.Comment: 6 page
K to pi and K to 0 in 2+1 Flavor Partially Quenched Chiral Perturbation Theory
We calculate results for K to pi and K to 0 matrix elements to
next-to-leading order in 2+1 flavor partially quenched chiral perturbation
theory. Results are presented for both the Delta I=1/2 and 3/2 channels, for
chiral operators corresponding to current-current, gluonic penguin, and
electroweak penguin 4-quark operators. These formulas are useful for studying
the chiral behavior of currently available 2+1 flavor lattice QCD results, from
which the low energy constants of the chiral effective theory can be
determined. The low energy constants of these matrix elements are necessary for
an understanding of the Delta I=1/2 rule, and for calculations of
epsilon'/epsilon using current lattice QCD simulations.Comment: 43 pages, 2 figures, uses RevTeX, added and updated reference
Saturation of dephasing time in mesoscopic devices produced by a ferromagnetic state
We consider an exchange model of itinerant electrons in a Heisenberg
ferromagnet and we assume that the ferromagnet is in a fully polarized state.
Using the Holstein-Primakoff transformation we are able to obtain a
boson-fermion Hamiltonian that is well-known in the interaction between light
and matter. This model describes the spontaneous emission in two-level atoms
that is the proper decoherence mechanism when the number of modes of the
radiation field is taken increasingly large, the vacuum acting as a reservoir.
In the same way one can see that the interaction between the bosonic modes of
spin waves and an itinerant electron produces decoherence by spin flipping with
a rate proportional to the size of the system. In this way we are able to show
that the experiments on quantum dots, described in D. K. Ferry et al. [Phys.
Rev. Lett. {\bf 82}, 4687 (1999)], and nanowires, described in D. Natelson et
al. [Phys. Rev. Lett. {\bf 86}, 1821 (2001)], can be understood as the
interaction of itinerant electrons and an electron gas in a fully polarized
state.Comment: 10 pages, no figure. Changed title. Revised version accepted for
publication in Physical Review
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