12,935 research outputs found
Sequential Desynchronization in Networks of Spiking Neurons with Partial Reset
The response of a neuron to synaptic input strongly depends on whether or not
it has just emitted a spike. We propose a neuron model that after spike
emission exhibits a partial response to residual input charges and study its
collective network dynamics analytically. We uncover a novel desynchronization
mechanism that causes a sequential desynchronization transition: In globally
coupled neurons an increase in the strength of the partial response induces a
sequence of bifurcations from states with large clusters of synchronously
firing neurons, through states with smaller clusters to completely asynchronous
spiking. We briefly discuss key consequences of this mechanism for more general
networks of biophysical neurons
Mass of Saturn's A ring
The mass of Saturn's A ring is reestimated using the behavior of spiral density waves embedded in the ring. The Voyager photopolarimeter (PPS) observed the star delta-Scorpii as it was occulted by Saturn's rings during the Voyager 2 flyby of Saturn in 1981 producing a radial profile of the rings. We examined forty spiral density waves in the Voyager PPS data of the A ring including 10 weaker waves that have not been previously analyzed by means of an autoregressive power spectral technique called Burg. The strengths of this new method for ring studies are that weaker, less extended waves are easily detected and characterized. This method is also the first one which does not require precise knowledge of the resonance location and phase of the wave in order to calculate the surface mass density. Uncertainties of up to 3 km are present in the currently available radial scales for Saturn's rings
Theory of impedance networks: The two-point impedance and LC resonances
We present a formulation of the determination of the impedance between any
two nodes in an impedance network. An impedance network is described by its
Laplacian matrix L which has generally complex matrix elements. We show that by
solving the equation L u_a = lambda_a u_a^* with orthonormal vectors u_a, the
effective impedance between nodes p and q of the network is Z = Sum_a [u_{a,p}
- u_{a,q}]^2/lambda_a where the summation is over all lambda_a not identically
equal to zero and u_{a,p} is the p-th component of u_a. For networks consisting
of inductances (L) and capacitances (C), the formulation leads to the
occurrence of resonances at frequencies associated with the vanishing of
lambda_a. This curious result suggests the possibility of practical
applications to resonant circuits. Our formulation is illustrated by explicit
examples.Comment: 21 pages, 3 figures; v4: typesetting corrected; v5: Eq. (63)
correcte
Investigating the timecourse of accessing conversational implicatures during incremental sentence interpretation
Many contextual inferences in utterance interpretation are explained as following from the nature of conversation and the assumption that participants are rational. Recent psycholinguistic research has focussed on certain of these ‘Gricean’ inferences and have revealed that comprehenders can access them in online interpretation. However there have been mixed results as to the time-course of access. Some results show that Gricean inferences can be accessed very rapidly, as rapidly as any other contextually specified information (Sedivy, 2003; Grodner, Klein, Carbery, & Tanenhaus, 2010); while other studies looking at the same kind of inference suggest that access to Gricean inferences are delayed relative to other aspects of semantic interpretation (Huang & Snedeker, 2009; in press). While previous timecourse research has focussed on Gricean inferences that support the online assignment of reference to definite expressions, the study reported here examines the timecourse of access to scalar implicatures, which enrich the meaning of an utterance beyond the semantic interpretation. Even if access to Gricean inference in support of reference assignment may be rapid, it is still unknown whether genuinely enriching scalar implicatures are delayed. Our results indicate that scalar implicatures are accessed as rapidly as other contextual inferences. The implications of our results are discussed in reference to the architecture of language comprehension
A note on the realignment criterion
For a quantum state in a bipartite system represented as a density matrix,
researchers used the realignment matrix and functions on its singular values to
study the separability of the quantum state. We obtain bounds for elementary
symmetric functions of singular values of realignment matrices. This answers
some open problems proposed by Lupo, Aniello, and Scardicchio. As a
consequence, we show that the proposed scheme by these authors for testing
separability would not work if the two subsystems of the bipartite system have
the same dimension.Comment: 11 pages, to appear in Journal of Physics A: Mathematical and
Theoretica
Pressure-induced insulator-to-metal transition in low-dimensional TiOCl
We studied the transmittance and reflectance of the low-dimensional
Mott-Hubbard insulator TiOCl in the infrared and visible frequency range as a
function of pressure. The strong suppression of the transmittance and the
abrupt increase of the near-infrared reflectance above 12 GPa suggest a
pressure-induced insulator-to-metal transition. The pressure-dependent
frequency shifts of the orbital excitations, as well as the pressure
dependences of the charge gap and the spectral weight of the optical
conductivity above the phase transition are presented.Comment: 4 pages, 6 figure
Unconventional elasticity in smectic-A elastomers
We study two aspects of the elasticity of smectic- elastomers that make
these materials genuinely and qualitatively different from conventional
uniaxial rubbers. Under strain applied parallel to the layer normal, monodomain
smectic- elastomers exhibit a drastic change in Young's modulus above a
threshold strain value of about 3%, as has been measured in experiments by
Nishikawa and Finkelmann [Macromol. Chem. Phys. {\bf 200}, 312 (1999)]. Our
theory predicts that such strains induce a transition to a smectic--like
state and that it is this transition that causes the change in elastic modulus.
We calculate the stress-strain behavior as well as the tilt of the smectic
layers and the molecular orientation for strain along the layer normal, and we
compare our findings with the experimental data. We also study the
electroclinic effect in chiral smectic- elastomers. According to
experiments by Lehmann {\em et al}. [Nature {\bf 410}, 447 (2001)] and
K\"{o}hler {\em et al}. [Applied Physics A {\bf 80}, 381 (2003)], this effect
leads in smectic- elastomers to a giant or, respectively, at least very
large lateral electrostriction. Incorporating polarization into our theory, we
calculate the height change of smectic- elastomer films in response to
a lateral external electric field, and we compare this result to the
experimental findings.Comment: 12 pages, 6 figure
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